Do not support universal wheels

[graingert]

because you need to build manylinux1/mac/windows wheels instead

[graingert]

although it's probably best to split this repo again into pure python and .c

[Byron]

As I am not quite sure about the impact of the C-code and the overall maintenance and distribution burden, I would rather remove it entirely.

In the current implementation using setup.py it would try to build the code, and just keep going on failure. Something like that I would love to have for the wheel as well.
Alternatively, maybe it's possible to keep supporting the setup.py for those who want to have a chance to improved performance, and those who use wheels will still get the python-only version.

I will just merge the commit for now, but do indeed hope there is a way to make this work.

[graingert]

I've pulled the C out into https://github.com/graingert/gitdb-speedups

This can now be optionally installed by those who need the speed

[Byron]

@graingert Thanks a lot - I have left a comment in the respective PR.