Clarify the purpose/use of the release number in ensembl_info.py

[grahamgower]

stdpopsim/catalog/ensembl_info.py currently shows the release number to be 103. This implies all species are at this release number. It also implies that when a new species is added, it should come from that same release. But our maintenance code doesn't support this---instead the new species will come from the most recent ensembl release, and the maintenance code will bump the release number. So now different species correspond to different release numbers. What number should be in ensembl_info.py?

Clearly we should not require that when a new species is added that all existing species get updated (in particular because an update can require recombination map liftover).

[jeromekelleher]

Clearly we should not require that when a new species is added that all existing species get updated (in particular because an update can require recombination map liftover).

You're right, the release number should be moved into the species data I guess. I had envisaged that we would periodically update the whole catalog to reflect the most recent data from Ensembl, but I hadn't imagined we were going to add this many species.