Enable setup.py to install cython if it isn't already.

[stuaxo]

Make python setup.py develop or python setup.py install install cython if it is not already.

Add install_requires with cython, (and make import completely optional).

[coveralls]

Coverage remained the same at 47.969% when pulling a7fc797 on stuaxo:patch-2 into dd7f4bf on swistakm:master.

[stuaxo]

@swistakm I'm not really sure what the error in appveyor is about, doesn't seem to be introduced by the patch though.

It seems like this bug in git-lfs

git-lfs/git-lfs#1697

Not sure if it is possible to upgrade git-lfs or is that something in appveyor ?

[swistakm]

Oh, yeah. This issue happens from time to time on AppVeyor and is caused by git-lfs. I've hit "rebuild" button.

[swistakm]

Once build passed we can start the discussion.

I did not add Cython to the package requirements rather on purpose. I primarily wanted to distribute both Cython .pyx and C++ .cpp sources as sdist package and leave the decision whether to use Cython or plain C++ compilation to the final user. This is actually a solution suggested by Cython documentation.

My general idea is to include both Cython and C++ sources in sdist package and trigger Cython installation using setuptools' extras_require option, e.g.:

pip install imgui[Cython]

Question is: should Cython existence (determined with try ... import block) be enough to trigger actual Cython compilation instead of plain C++ compilation? I think we should be fine with this. What do you think @stuaxo? We can always add additional environment variable later to enable/disable such behaviour.

Still, I will merge this PR because we will have to use this cythonize() function stub anyway but I will remove the install_requires and setup_requires soon.

[stuaxo]

That all sounds really sensible. We should be fine with the try... import + optional environment variable.