Robolectric annotation processor - rebased

This is a rebased version of PR #1224. Hopefully it will pass the Travis build.
I have no problems with removing it (though I am curious as to what you think the inaccuracies are). Basically what I wanted to say was that the earlier in the development cycle you catch bugs, the more efficient your development cycle becomes, and that the Robolectric Annotation Processor aids in this goal.

I'll simplify it a bit and update my branch for you to comment on further.