This improves on the original fix to #5285 by preventing
other mixed lists (lists with a mix of Plain and Para
elements) that were allowed given the original fix.
- 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.
This is now the default for pandoc's Markdown.
It allows whitespace between the two parts of a
reference link: e.g.
[a] [b]
[b]: url
This is now forbidden by default.
Closes#2602.
