Python cffi bindings

It would be handy to have pure c cffi python bindings that don't require c++ for use on both embedded systems that don't build a c++ toolchain and for pypy which performs best using cffi instead of cpython extensions. The unmaintained [brotlipy](https://github.com/python-hyper/brotlipy) fork has cffi bindings that could be adapted for this project as a build option.