Add support for using the modularized passagemath distributions

[mkoeppe]

pip install .[passagemath] installs snappy with the modularized distributions providing the needed parts of the Sage library.

To test: tox

[mkoeppe]

Currently

$ tox
[...]
Collecting snappy_manifolds>=1.2.1
  Using cached snappy_manifolds-1.2.1-py3-none-any.whl.metadata (1.5 kB)
ERROR: Could not find a version that satisfies the requirement spherogram>=2.3 (from versions: 1.3, 1.4, 1.4.1, 1.5, 1.5.1, 1.5.2, 1.5.5, 1.6, 1.6.1, 1.7, 1.8, 1.8.1, 1.8.2, 1.8.3, 2.0, 2.1, 2.2, 2.2.1)
ERROR: No matching distribution found for spherogram>=2.3

passagemath: exit 1 (1.27 seconds) /Users/mkoeppe/s/sage/SnapPy> python -I -m pip install 'FXrays>=1.3' PyX 'cypari>=2.3' decorator 'ipython>=5.0' 'low_index>=1.2.1' packaging pickleshare 'plink>=2.4.3' pypng 'snappy_manifolds>=1.2.1' 'spherogram>=2.3' 'tkinter-gl>=1.0' pid=6428

[NathanDunfield]

Spherogram 2.3 was just posted to PyPI, so tox should work again.

[mkoeppe]

Thanks!