Previously these were always escaped and printed verbatim.
Now they are ignored unless the format is "icml", in which
case they are passed through unescaped.
Closes#1951.
Previously text that ended a div would be parsed as Plain
unless there was a blank line before the closing div tag.
Test case:
<div class="first">
This is a paragraph.
This is another paragraph.
</div>
Closes#1591.
- We no longer include trailing spaces and newlines in the
raw blocks.
- We look for closing tags for elements (but without backtracking).
- Each block-level tag is its own RawBlock; we no longer try to
consolidate them (though `--normalize` will do so).
Closes#1330.
