Upgrade to LLVM 3.5

 - Fix fd_raw_ostream constructor call
   See https://github.com/llvm-mirror/llvm/commit/8c968628473c7de416e3f468fead20023f33107e

 - Fix build error in LoadFromASTFile constructor call

 - Rename getResultType() on function and method declarations to getReturnType()
   See https://github.com/llvm-mirror/clang/commit/37545f747c61382bbf5291d28a47fef6fc4d2d0e

 - Update Cmake download url to LLVM 3.5

 - Update documentation.