Markdown definition lists: don't require indent for first line.

Previously the body of the definition (after the `:` or `~` marker)
needed to be in column 4.  This commit relaxes that requirement,
to better match the behavior of PHP Markdown Extra.  So, now
this is a valid definition list:

    foo
    : bar

This patch also helps resolve a potentially ambiguity with table
captions:

    foo

      : bar

      -----
      table
      -----

Is "bar" a definition, or the caption for the table?  We'll count
it as a caption for the table.

Closes #2087.

1 files changed, 3 insertions, 0 deletions

diff --git a/tests/Tests/Readers/Markdown.hs b/tests/Tests/Readers/Markdown.hs
index 8965d1d6e..aaeefcfa4 100644
--- a/tests/Tests/Readers/Markdown.hs
+++ b/tests/Tests/Readers/Markdown.hs
@@ -270,6 +270,9 @@ tests = [ testGroup "inline code"
             definitionList [ (text "foo1", [para (text "bar") <>
                                             para (text "baz")])
                            ]
+          , "first line not indented" =:
+            "foo\n: bar\n" =?>
+            definitionList [ (text "foo", [plain (text "bar")]) ]
           ]
         , testGroup "+compact_definition_lists"
           [ test markdownCDL "basic compact list" $