Add version information at runtime

Created by: Zaharid

It would be useful to output version information at runtime. This is to make it possible to reproduce results based on old code even after breaking compatibility with the input (which we try not to do very much).

We want:

• Version retrieved from git during development. This would be git describe --tags --dirty or similar, processed to match the conda package.
• Version stored in the package, ideally matching the format of the conda package.

This could be accomplished with a file, version.py, where the __version__ is queried from git during development but the file is replaced with a hardcoded string for __version__ when the package is constructed.

I have looked several times at https://github.com/msztolcman/versionner, but seems a little too complicated.