Previously we tried to handle things like commented out list
items:
- one
<!--
- two
-->
- three
and also things like:
- one `and
- two` and
But the code we added to handle these cases caused problems with
other, more straightforward things, like:
- one
- ```
code
```
- three
So we are rolling back all the fanciness, so that the markdown
parser now behaves more like the commonmark parser, in which
indicators of block-level structure always take priority over
indicators of inline structure.
Closes#9865. Closes#7778. See also #5628.
