Turn modes into module constants

That is the closest I can get to exposing enums to Python, better that
doing text comparison at least.
Rename as brotli.cc to brotlimodule.cc

In preparation for merging with main Brotli repository.
Port to Python 3
Add some more metadata
Formatting
updated brotli submodule
update brotli submodule
update brotli submodule