experimenting with milestones at github

[Lubomir I. Ivanov]

a milestone can be used to distinguish issues and PRs that are
targeting a release.
for example, we already released 4.8, but all 4.8.x issues and PRs
should have the same 4.8 milestone.

i've added the 4.8 milestone at github and assigned one issue for it for now:
https://github.com/Subsurface-divelog/subsurface/issues/1461

here are a couple of other bugs that could be fixed in 4.8.1 as well:
https://github.com/Subsurface-divelog/subsurface/issues/1445
https://github.com/Subsurface-divelog/subsurface/issues/1446

if you think there are more, we can add them.

lubomir
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