Allow em for image height/width in HTML, LaTeX.

- Export `inEm` from ImageSize [API change].
- Change `showFl` and `show` instance for `Dimension` so
  extra decimal places are omitted.
- Added `Em` as a constructor of `Dimension` [API change].
- Allow `em`, `cm`, `in` to pass through without conversion
  in HTML, LaTeX.

Closes #3450.

3 files changed, 48 insertions, 36 deletions

diff --git a/test/command/3450.md b/test/command/3450.md
new file mode 100644
index 000000000..8759aa0c1
--- /dev/null
+++ b/test/command/3450.md
@@ -0,0 +1,12 @@
+```
+% pandoc -fmarkdown-implicit_figures
+![image](lalune.jpg){height=2em}
+^D
+<p><img src="lalune.jpg" alt="image" style="height:2em" /></p>
+```
+```
+% pandoc -fmarkdown-implicit_figures -t latex
+![image](lalune.jpg){height=2em}
+^D
+\includegraphics[height=2em]{lalune.jpg}
+```
diff --git a/test/command/svg.md b/test/command/svg.md
index 36ca2fdb7..b48745f9a 100644
--- a/test/command/svg.md
+++ b/test/command/svg.md
@@ -5,20 +5,20 @@
 [warning] Could not determine image size for 'command/corrupt.svg': could not determine image type
 <ParagraphStyleRange AppliedParagraphStyle="ParagraphStyle/Paragraph">
   <CharacterStyleRange AppliedCharacterStyle="$ID/NormalCharacterStyle">
-    <Rectangle Self="uec" StrokeWeight="0" ItemTransform="1.00000 0 0 1.00000 150.00000 -100.00000">
+    <Rectangle Self="uec" StrokeWeight="0" ItemTransform="1 0 0 1 150 -100">
       <Properties>
         <PathGeometry>
           <GeometryPathType PathOpen="false">
             <PathPointArray>
-              <PathPointType Anchor="-150.00000 -100.00000" LeftDirection="-150.00000 -100.00000" RightDirection="-150.00000 -100.00000" />
-              <PathPointType Anchor="-150.00000 100.00000" LeftDirection="-150.00000 100.00000" RightDirection="-150.00000 100.00000" />
-              <PathPointType Anchor="150.00000 100.00000" LeftDirection="150.00000 100.00000" RightDirection="150.00000 100.00000" />
-              <PathPointType Anchor="150.00000 -100.00000" LeftDirection="150.00000 -100.00000" RightDirection="150.00000 -100.00000" />
+              <PathPointType Anchor="-150 -100" LeftDirection="-150 -100" RightDirection="-150 -100" />
+              <PathPointType Anchor="-150 100" LeftDirection="-150 100" RightDirection="-150 100" />
+              <PathPointType Anchor="150 100" LeftDirection="150 100" RightDirection="150 100" />
+              <PathPointType Anchor="150 -100" LeftDirection="150 -100" RightDirection="150 -100" />
             </PathPointArray>
           </GeometryPathType>
         </PathGeometry>
       </Properties>
-      <Image Self="ue6" ItemTransform="1.00000 0 0 1.00000 -150.00000 -100.00000">
+      <Image Self="ue6" ItemTransform="1 0 0 1 -150 -100">
         <Properties>
           <Profile type="string">
             $ID/Embedded
@@ -38,20 +38,20 @@
 [warning] Could not determine image size for 'command/SVG_logo.svg': could not determine SVG size
 <ParagraphStyleRange AppliedParagraphStyle="ParagraphStyle/Paragraph">
   <CharacterStyleRange AppliedCharacterStyle="$ID/NormalCharacterStyle">
-    <Rectangle Self="uec" StrokeWeight="0" ItemTransform="1.00000 0 0 1.00000 150.00000 -100.00000">
+    <Rectangle Self="uec" StrokeWeight="0" ItemTransform="1 0 0 1 150 -100">
       <Properties>
         <PathGeometry>
           <GeometryPathType PathOpen="false">
             <PathPointArray>
-              <PathPointType Anchor="-150.00000 -100.00000" LeftDirection="-150.00000 -100.00000" RightDirection="-150.00000 -100.00000" />
-              <PathPointType Anchor="-150.00000 100.00000" LeftDirection="-150.00000 100.00000" RightDirection="-150.00000 100.00000" />
-              <PathPointType Anchor="150.00000 100.00000" LeftDirection="150.00000 100.00000" RightDirection="150.00000 100.00000" />
-              <PathPointType Anchor="150.00000 -100.00000" LeftDirection="150.00000 -100.00000" RightDirection="150.00000 -100.00000" />
+              <PathPointType Anchor="-150 -100" LeftDirection="-150 -100" RightDirection="-150 -100" />
+              <PathPointType Anchor="-150 100" LeftDirection="-150 100" RightDirection="-150 100" />
+              <PathPointType Anchor="150 100" LeftDirection="150 100" RightDirection="150 100" />
+              <PathPointType Anchor="150 -100" LeftDirection="150 -100" RightDirection="150 -100" />
             </PathPointArray>
           </GeometryPathType>
         </PathGeometry>
       </Properties>
-      <Image Self="ue6" ItemTransform="1.00000 0 0 1.00000 -150.00000 -100.00000">
+      <Image Self="ue6" ItemTransform="1 0 0 1 -150 -100">
         <Properties>
           <Profile type="string">
             $ID/Embedded
@@ -71,20 +71,20 @@
 [warning] Could not determine image size for 'command/SVG_logo-without-xml-declaration.svg': could not determine SVG size
 <ParagraphStyleRange AppliedParagraphStyle="ParagraphStyle/Paragraph">
   <CharacterStyleRange AppliedCharacterStyle="$ID/NormalCharacterStyle">
-    <Rectangle Self="uec" StrokeWeight="0" ItemTransform="1.00000 0 0 1.00000 150.00000 -100.00000">
+    <Rectangle Self="uec" StrokeWeight="0" ItemTransform="1 0 0 1 150 -100">
       <Properties>
         <PathGeometry>
           <GeometryPathType PathOpen="false">
             <PathPointArray>
-              <PathPointType Anchor="-150.00000 -100.00000" LeftDirection="-150.00000 -100.00000" RightDirection="-150.00000 -100.00000" />
-              <PathPointType Anchor="-150.00000 100.00000" LeftDirection="-150.00000 100.00000" RightDirection="-150.00000 100.00000" />
-              <PathPointType Anchor="150.00000 100.00000" LeftDirection="150.00000 100.00000" RightDirection="150.00000 100.00000" />
-              <PathPointType Anchor="150.00000 -100.00000" LeftDirection="150.00000 -100.00000" RightDirection="150.00000 -100.00000" />
+              <PathPointType Anchor="-150 -100" LeftDirection="-150 -100" RightDirection="-150 -100" />
+              <PathPointType Anchor="-150 100" LeftDirection="-150 100" RightDirection="-150 100" />
+              <PathPointType Anchor="150 100" LeftDirection="150 100" RightDirection="150 100" />
+              <PathPointType Anchor="150 -100" LeftDirection="150 -100" RightDirection="150 -100" />
             </PathPointArray>
           </GeometryPathType>
         </PathGeometry>
       </Properties>
-      <Image Self="ue6" ItemTransform="1.00000 0 0 1.00000 -150.00000 -100.00000">
+      <Image Self="ue6" ItemTransform="1 0 0 1 -150 -100">
         <Properties>
           <Profile type="string">
             $ID/Embedded
@@ -104,20 +104,20 @@
 ^D
 <ParagraphStyleRange AppliedParagraphStyle="ParagraphStyle/Paragraph">
   <CharacterStyleRange AppliedCharacterStyle="$ID/NormalCharacterStyle">
-    <Rectangle Self="uec" StrokeWeight="0" ItemTransform="1.00000 0 0 1.00000 54.75000 -65.25000">
+    <Rectangle Self="uec" StrokeWeight="0" ItemTransform="1 0 0 1 54.75 -65.25">
       <Properties>
         <PathGeometry>
           <GeometryPathType PathOpen="false">
             <PathPointArray>
-              <PathPointType Anchor="-54.75000 -65.25000" LeftDirection="-54.75000 -65.25000" RightDirection="-54.75000 -65.25000" />
-              <PathPointType Anchor="-54.75000 65.25000" LeftDirection="-54.75000 65.25000" RightDirection="-54.75000 65.25000" />
-              <PathPointType Anchor="54.75000 65.25000" LeftDirection="54.75000 65.25000" RightDirection="54.75000 65.25000" />
-              <PathPointType Anchor="54.75000 -65.25000" LeftDirection="54.75000 -65.25000" RightDirection="54.75000 -65.25000" />
+              <PathPointType Anchor="-54.75 -65.25" LeftDirection="-54.75 -65.25" RightDirection="-54.75 -65.25" />
+              <PathPointType Anchor="-54.75 65.25" LeftDirection="-54.75 65.25" RightDirection="-54.75 65.25" />
+              <PathPointType Anchor="54.75 65.25" LeftDirection="54.75 65.25" RightDirection="54.75 65.25" />
+              <PathPointType Anchor="54.75 -65.25" LeftDirection="54.75 -65.25" RightDirection="54.75 -65.25" />
             </PathPointArray>
           </GeometryPathType>
         </PathGeometry>
       </Properties>
-      <Image Self="ue6" ItemTransform="1.00000 0 0 1.00000 -54.75000 -65.25000">
+      <Image Self="ue6" ItemTransform="1 0 0 1 -54.75 -65.25">
         <Properties>
           <Profile type="string">
             $ID/Embedded
diff --git a/test/writer.icml b/test/writer.icml
index c39915120..6e070e264 100644
--- a/test/writer.icml
+++ b/test/writer.icml
@@ -2833,20 +2833,20 @@ These should not be escaped:  \$ \\ \&gt; \[ \{</Content>
 <Br />
 <ParagraphStyleRange AppliedParagraphStyle="ParagraphStyle/Figure">
   <CharacterStyleRange AppliedCharacterStyle="$ID/NormalCharacterStyle">
-    <Rectangle Self="uec" StrokeWeight="0" ItemTransform="1.00000 0 0 1.00000 75.00000 -75.00000">
+    <Rectangle Self="uec" StrokeWeight="0" ItemTransform="1 0 0 1 75 -75">
       <Properties>
         <PathGeometry>
           <GeometryPathType PathOpen="false">
             <PathPointArray>
-              <PathPointType Anchor="-75.00000 -75.00000" LeftDirection="-75.00000 -75.00000" RightDirection="-75.00000 -75.00000" />
-              <PathPointType Anchor="-75.00000 75.00000" LeftDirection="-75.00000 75.00000" RightDirection="-75.00000 75.00000" />
-              <PathPointType Anchor="75.00000 75.00000" LeftDirection="75.00000 75.00000" RightDirection="75.00000 75.00000" />
-              <PathPointType Anchor="75.00000 -75.00000" LeftDirection="75.00000 -75.00000" RightDirection="75.00000 -75.00000" />
+              <PathPointType Anchor="-75 -75" LeftDirection="-75 -75" RightDirection="-75 -75" />
+              <PathPointType Anchor="-75 75" LeftDirection="-75 75" RightDirection="-75 75" />
+              <PathPointType Anchor="75 75" LeftDirection="75 75" RightDirection="75 75" />
+              <PathPointType Anchor="75 -75" LeftDirection="75 -75" RightDirection="75 -75" />
             </PathPointArray>
           </GeometryPathType>
         </PathGeometry>
       </Properties>
-      <Image Self="ue6" ItemTransform="1.00000 0 0 1.00000 -75.00000 -75.00000">
+      <Image Self="ue6" ItemTransform="1 0 0 1 -75 -75">
         <Properties>
           <Profile type="string">
             $ID/Embedded
@@ -2869,20 +2869,20 @@ These should not be escaped:  \$ \\ \&gt; \[ \{</Content>
     <Content>Here is a movie </Content>
   </CharacterStyleRange>
   <CharacterStyleRange AppliedCharacterStyle="$ID/NormalCharacterStyle">
-    <Rectangle Self="uec" StrokeWeight="0" ItemTransform="1.00000 0 0 1.00000 10.00000 -11.00000">
+    <Rectangle Self="uec" StrokeWeight="0" ItemTransform="1 0 0 1 10 -11">
       <Properties>
         <PathGeometry>
           <GeometryPathType PathOpen="false">
             <PathPointArray>
-              <PathPointType Anchor="-10.00000 -11.00000" LeftDirection="-10.00000 -11.00000" RightDirection="-10.00000 -11.00000" />
-              <PathPointType Anchor="-10.00000 11.00000" LeftDirection="-10.00000 11.00000" RightDirection="-10.00000 11.00000" />
-              <PathPointType Anchor="10.00000 11.00000" LeftDirection="10.00000 11.00000" RightDirection="10.00000 11.00000" />
-              <PathPointType Anchor="10.00000 -11.00000" LeftDirection="10.00000 -11.00000" RightDirection="10.00000 -11.00000" />
+              <PathPointType Anchor="-10 -11" LeftDirection="-10 -11" RightDirection="-10 -11" />
+              <PathPointType Anchor="-10 11" LeftDirection="-10 11" RightDirection="-10 11" />
+              <PathPointType Anchor="10 11" LeftDirection="10 11" RightDirection="10 11" />
+              <PathPointType Anchor="10 -11" LeftDirection="10 -11" RightDirection="10 -11" />
             </PathPointArray>
           </GeometryPathType>
         </PathGeometry>
       </Properties>
-      <Image Self="ue6" ItemTransform="1.00000 0 0 1.00000 -10.00000 -11.00000">
+      <Image Self="ue6" ItemTransform="1 0 0 1 -10 -11">
         <Properties>
           <Profile type="string">
             $ID/Embedded