Markdown reader/writer: spacing adjustments in tables.

* Markdown writer now includes a blank line at the end
  of the row in a single-row multiline table, to prevent it from being
  interpreted as a simple table.  Closes #4578.
* Markdown reader does a better job computing the relative width of
  the last column in a multiline table, so we can round-trip tables
  without constantly shrinking the last column.

1 files changed, 14 insertions, 0 deletions

diff --git a/test/command/4578.md b/test/command/4578.md
new file mode 100644
index 000000000..8f12d0bf2
--- /dev/null
+++ b/test/command/4578.md
@@ -0,0 +1,14 @@
+```
+% pandoc -t markdown
+  ------ ------- --------------- ---------------------
+  One    row                12.0 Example of a row that
+                                 spans multiple lines.
+
+  ------ ------- --------------- ---------------------
+^D
+  ------ ------- --------------- ---------------------
+  One    row                12.0 Example of a row that
+                                 spans multiple lines.
+
+  ------ ------- --------------- ---------------------
+```