Should switch from tag-triggered releases to manually triggered

[smheidrich]

Triggering on tags causes nothing but problems, where if something about the CI build breaks (and it inevitably does), you have to delete and reupload the tag, and then if only half of the wheels were uploaded (e.g. the ones built on GitHub but not the ones on CircleCI), after fixing that and moving the tag, it looks like the other half failed when in fact that was just PyPI rejecting the reupload etc.

If possible, should just have manual triggers for this on GitHub and CircleCI and be done with it...