Version number should be inferred from git tag

[mjuric]

Right now, the version number is hardcoded in setup.py; every time one makes a release one needs to remember to manually update it.

It'd be better to use something like setuptools_scm to automatically infer the version number from git.

This issue is to make sure we don't forget about it.

[mjuric]

Oh, I see the update_version.py script now; I'll look into how/what it does.