#32 Only process markdown

[alf239]

Hi Or,

I'm not quite sure you want that change — as far as I can tell, it changes semantics a lot; still, it may be useful, so if you need it, here's it :)

Basically, many source files have $ signs where they are not meant to mean $\LaTeX\ here!$ — e.g. Scala's interpolated strings:

val name = "World"
println(s"Hello $name! How are you, $name?")

I also added support for the PR dialog preview tab — its selection class was changed,