Improve the Markdown escaping logic.
This improves our Markdown escaping to better handle parens,

underscores, and asterisks.
The common cases of showing function names with parens and underscores

should no longer result in a bunch of escaping. We now do a better job

of escaping only when they're going to cause formatting changes.
Since some of the regexes were getting a bit longer, I've also

repositioned the comments in the regexes to appear before the regex

lines.

Unit tests pass.
Posting a change with a bunch of formatting, some that should be

escaped and some that shouldn't. This included functions like

this_is_a_test(). The contents were preserved and not escaped.