Initial version of formatting library.

This formatting library will be used by a stand-alone clang-format tool
and can also be used when writing other refactorings.

Manuel's original design document:
https://docs.google.com/a/google.com/document/d/1gpckL2U_6QuU9YW2L1ABsc4Fcogn5UngKk7fE5dDOoA/edit

The library can already successfully format itself.

Review: http://llvm-reviews.chandlerc.com/D80
llvm-svn: 169137