Add setup.py to be pip installable

[hugovk]

For #32.

To test locally, note the command is simply heatmap rather than heatmap.py:

pip install -e .
heatmap test/few-points -o map.png --width 100

Notes:

• An __init__.py file isn't needed
• I don't know what name you'd like, this uses "sethoscope-heatmap" just for testing
• Version number has a .dev0 suffix to differentiate dev versions. The idea is to remove this for the release, then increment and add back. But you could leave it off if you prefer.
• You can choose classifiers from https://pypi.org/pypi?%3Aaction=list_classifiers
• No need for requirements.txt, they're included in setup.py

[coveralls]

Coverage decreased (-0.05%) to 78.85% when pulling e747550 on hugovk:setuppable into ea0587c on sethoscope:master.

[coveralls]

Coverage remained the same at 78.925% when pulling 5fdb00c on hugovk:setuppable into 5cccdcd on sethoscope:master.

[coveralls]

Coverage remained the same at 78.925% when pulling 5fdb00c on hugovk:setuppable into 5cccdcd on sethoscope:master.

[hugovk]

Renamed to suggest heatmap-cli

It's available: https://pypi.org/project/heatmap-cli/

It would also possible to auto-deploy tagged versions to PyPI with something like this.

[hugovk]

If there's any interest in this, I'd be happy to update to use pyproject.toml, but I think 5.5 years was long enough to keep this one open :)