tags not merged to master lead to wrong dev tags and pip incompatibilites

Reminder issue @colm.talbot as discussed in this chat thread:

When doing pip install . or similar from a git checkout, or pip install git+ssh://git@git.ligo.org/lscsoft/bilby.git, one gets versions like 2.1.2.dev27+ged8ca671. Here the x.y.z number comes from the last tag in the past of the current branch head. Unfortunately, when tags are not merged to master, this means that they are ignored for this scheme. (In the current example, 2.1.2 was already released, so the version string should start with 2.1.3.dev, but the 2.1.2 tag points to a git hash not on master.) Since pep440 seems to imply that a 2.1.2.dev tag is for dev versions before 2.1.2 itself, this then fails the bilby_pipe dependency of bilby>=2.1.2.

The versioning scheme seems correct for pep440 and the dependency check, though unintuitive, also apparently works according to spec. So the only solution seems to me to be a change to the release branch model, were tagged versions are eventually merged back into master. lscsoft/lalsuite could be looked at as a model.