Deprecate in favor of Alabaster

[introt]

Alabaster is maintained once more, and it's time for alabester to be put to rest - but how?

Adding a DeprecationWarning on import and publishing a new version with Development Status :: 7 - Inactive is a start, but is there a proper Right Way?

[introt]

For reference: sphinx-doc#174 (comment)

[introt]

Build workflow seems to still work, so pushing a new version should be pretty straight forward.

https://github.com/introt/alabester/actions/runs/10393302640/job/28780474031