Update clang python binding to 6.0.0

[SuperBo]

The latest python binding in llvm 6.0.0 has support for python3. We don't need to use an in-house library like libclang-python3 any more.

These files are taken directly from clang source code from http://releases.llvm.org/6.0.0/cfe-6.0.0.src.tar.xz However, this source code has small bugs when used with deoplete-clang. So I fix the bug and attached the patch file for more information.

clang-python.patch

[Shougo]

It should be merged.

@zchee Ping.