Markdown support

+ Markdown support
+ Prompt when unsaved changes

While this works, I'm not sure if this is the best approach. It might be better to stick all the configuration and logic inside `base.php`, as it'd be more likely that someone would implement a new `provider/*` than a new editor.

Thoughts?
    $ grep -r mysql . | wc -l
    92

Welp. I've fixed these two instances for now, but I'll hold off on using mysqli for when I'm sufficiently bored. :)