Update to CodeMirror 1.20, and enable auto-continuation of lists.
This updates CodeMirror to 1.20, which has some fixes for lists in

Markdown (in particular, bullet points at the beginning of a list

sometimes turning into emphasis).
It also enables auto-continuation of lists. For example, starting a line

with "* blah" and hitting enter will start the next line off with a new

list item. This works for ordered and unordered lists.

Couldn't reproduce the list bug anymore that I was hitting. That was reproduceable by:
This is a *test*
* This line ended up with emphasis.

Also tested that list continuation worked well.
Didn't see any regressions.
Note that I didn't include the new build of CodeMirror in the diff, but it's in my

change.