TOC improvements

1) Highlight current file in the dropdown
2) Make dropdown expand also from keyboard
3) Display links in TOC as block so they get 100% width

Ad 1, I've made it with inline javascript at the end of the file but this is rather a hack, would be better to do this in jade at build time, but my eyes bleed when I read Jade templates (and yes, I'm a noob too :P)
So, before integrating, should be checked if this doesn't break IE etc., or to rewrite it as a build-time thing.

Ad 2, dropdown can be expanded from keyboard, but the items on the list are not TAB-navigable, which actually might be a good thing (getting through 50 links before having the real content reachable can be boring). However, when the dropdown is made visible via tabbing, AND one clicks some non-TAB button then, then the items from the list are accessible via subsequently tabbing (the issue is that the dropdown appears only on  `:active` of a parent, and the TAB-order is probably evaluated beforehand).