Use fontTools.cu2qu instead of cu2qu

[simoncozens]

According to googlefonts/cu2qu#191, cu2qu (the independent Python module) has ceased development and has now been folded into fontTools. This PR changes ufo2ft to use the fontTools version.

[anthrotype]

We didn't replace it yet intentionally, because the standalone cu2qu is accelerated using cython the fonttools one is pure python thus slower. The two modules are still in sync, no new features was added in the fonttools copy that warrants losing the speed-up.
Why do you want to do this now?

[anthrotype]

If you like we could make it optional, have ufo2ft first try to import the standalone cu2qu and then fall back to fonttools cu2qu. But I want to understand the reason first

[simoncozens]

The issue I linked suggests that the standalone module is dead and replaced by fontTools, so I thought it would make sense to use the not-dead implementation. I didn’t know about the Cython optimisation. I agree it would be a shame to lose that. I wonder why it wasn’t brought over.

[anthrotype]

I wonder why it wasn’t brought over.

Actually it was! But it's only enabled if you build fonttools from source and you have cython already installed, or if you explicitly pass an optional build-time flag to fonttools setup.py (--with-cython or exporting FONTTOOLS_WITH_CYTHON=1 environment variable). We didn't enable this by default for the standard fonttools wheel package that we distribute over PyPI because we wanted to keep the traditional pure-python-ness of fonttools.

[bkmgit]

It would likely be good for the environment to enable Cython optimization in fonttools to minimize software energy consumption.

[anthrotype]

this has already happened so can be closed