Improve installation process [pip-extras]

[alwavshumilin]

Greetings! Straight to the point, got some problems with installation whenever I want to use cythonised version of this handy package. Since pip doesn't guarantee installation order it's a little bit tricky for doing everything right and keep requirements clean and tidy. Was wondering if one mind me (or someone else) adding "extras" section for setup.py, so it will be possible to install Cython before package binaries only when specific flag is given.

Pip already can install things correctly based on topological order, we want to use that feature :)

[grantjenks]

I've just released v2.0.0 to PyPI and it includes pre-built binary wheels. Will that work for you or is this still an issue?

I'm otherwise open to an "extras" section for Cython but it'll take some learning on my part.