Fix setup.py

[helkhalfi]

Hello,
I tried to pip install this library, but I faced that setup.py is not existing
Let me know if you have any questions regarding this PR (we use heavily PyPy ;) on our platform) and also if you can add it to PyPi so we other can use it without pointing pip to github 👍 (happy to help on this topic)

Thank you very much

[helkhalfi]

@swapniel99 @wc-duck @maogm12 @garnel
Hello there, please if you can take a look at this PR :)

[wc-duck]

I'm personally not that big of a python user these days, and by that not that knowledgeable about pip and what is needed for that.
pymmh3 was designed as a copy-into-your-codebase kind of library.
Do you really need a package-manager for such a simple file/lib?
I would like some more info on this before merging (note that I will accept this if it makes peoples life easier). I will however not maintain this on PyPi as I think this is easy enough to just copy. Feel free to distribute it yourself though.