Epoch operator

[remkade]

This adds support for the Python style version Epochs.

These are intended to allow developers to change their versioning scheme but also still maintain version ordering. More details here: https://peps.python.org/pep-0440/#version-epochs

I implemented this by adding a new Manifest option called epoch: bool and then adding logic to the fn split_version_str() to check for the presence of that epoch manifest option and inject a default manifest version of 0 if necessary.

[timvisee]

Sweet. Thanks for implementing!

I'd like to merge this in about a week. Is that okay, or would you like to see this ASAP?

[remkade]

No urgency, feel free to merge whenever!