Store version in a separate module

[ritiek]

This allows us to read version from setup.py before dependencies are installed.

Addresses #252.

[alastair]

Thanks for the recommendation. I'm a bit worried about using exec() in the setup file, perhaps it'd be better to use something like setuptools-scm or versioneer. Do you have experience with either of them? I've got experience with using setuptools-scm in some other projects, so I think that'd be a good choice. I believe that setuptools v42 (the version required for this feature) still supports python 2, so that'd be good to go for. While we should remove python 2 support soon, I'd like to do 1 more release supporting it first.

[ritiek]

Thanks for the recommendation. I'm a bit worried about using exec() in the setup file, perhaps it'd be better to use something like setuptools-scm or versioneer. Do you have experience with either of them?

I think exec() might not be so bad here, although I'm not very sure myself either. I haven't tried out setuptools-scm or versioneer yet. This looks like a trade-off between uncertainty and adding a new dependency, so completely up to you what seems like a better idea.