support optional gitdb_speedups

[graingert]

No description provided.

[Byron]

Thanks a lot ! I have forked https://github.com/gitpython-developers/gitdb-speedups for now, in preparation for getting it released.
Would you be OK transferring ownership of said repository to gitpython-developers ? If so, I would just have to delete the fork to make this work.

@ankostis I am having massive difficulty to keep up with the pipy-to-wheels transformations, primarily due to me having hard feelings against the entire pypi platform (I mean, they managed to simply not migrate their google users until it was too late, making them loose ownership on their packages ... how bad can you be ?). Thus I would love it if you could take over handling all pypi related things. If you agree, all I would need is your pypi username.