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.

0 files changed, 0 insertions, 0 deletions