ENH: Add support for and ability to force markdown

Just about every technology community forum I use nowadays uses markdown for the editor. Probably because support for code insertions is super easy. Also, largely due to Github, it has become the standard. HTML WYSIWYG editors are, at best, OK for a general audience. But most of the time they suck.

What I'd love to see is that the entire module can be switched to "only" markdown. It would entail having a field in the posts table to indicate what format the contents are in. Plain text, markdown, html. There are great libraries both server side and client side that can convert MD to HTML.