How to map versions

[fingolfin]

For the JLLs (GAP_pkg_*_jll) the pattern is to map GAP version 1.2.3 to 100.200.300, plus potentially an offset. This decouples the GAP version from the Julia version a bit and gives us room to update the wrapper packages even if the underlying GAP packages have not changed.

• should we adopt a similar scheme for the wrappers here in this repository?
• how to deal with package versions like 2021.04-03 (used by Homalg and CAP these days)?
• in the past, some packages had versions like 1.0c. I don't think that is the case for anything right now, but perhaps the GAP side should start to impose tighter constraints on version patterns?
• GAP packages don't follow semver, so we may need to take that into account, too..