Esprima

In this pull request I redid my previous work with esprima instead of acorn. I think things work better this way thanks to esprima's richer feature set, on the other-hand it's a bit slower now. (I don't know if the performance loss is actually a problem, give it a a try and let's see)
I added annotation for variables and properties too, so now most usecases should be covered.
Anyway, any feedback is welcome and maybe this could be a base for a more stable annotation-extension...