Add semantic release tags?

[gdevenyi]

Currently this repo has no "versions"

[larsoner]

Nowadays many repos (including mne-python)R use dynamic versioning. That is, the package.__version__ is figured out by the packaging system based on tagged releases and a given versioning scheme (usually semantic).

At the end of the day, it reduces maintenance burden because you can just create a new tag from master on GitHub -- often/ideally by cutting a release using the UI -- and that ends up landing as the mod.__version__. I'm happy to implement this if it would help