Merge pull request #369 from klickverbot/shorten-readme

Shorten readme
Stop running Travis tests using LLVM 3.0.

Sets the stage for removal of 3.0 support.
Removed LLVM 3.0 compatibility code.

There might be still some pieces left here and there, and
there is certainly code that could be rewritten in a nicer
way with the 3.0 requirement out of the picture.
Removed LLVM support from druntime as well.