Add support for tab characters

[Possseidon]

I personally don't like tabs, but I guess a proper editor should support them after all... I should keep in mind that there are a bunch of places where I hardcoded spaces that should also include tabs (just use %s).

I'm not even sure what happens at the moment if you open a file with tabs.

[Possseidon]

Update: Currently it simply renders tab characters as a single whitespace. I mean, it's nice that it at least seems to not go up in flames, but support could definitely be improved here.