Release tag naming scheme

[shawnlaffan]

It would be useful to settle on a naming scheme for the tags used to flag releases. This is not urgent but would be nice to have clarified.

So far I've been using a somewhat ad-hoc system with parts being accreted as they seem to make sense, e.g. the latest release is SP_54001_64bit_UCRT.

Eventually the UCRT in the name will be unnecessary as it becomes the default but we might yet release a UCRT version of 5.38.2, and 5.38.3 will ideally do so if one is released.

Similar logic applies to the 64bit component but it could be argued that a future version might use long doubles (although the last version to do so was 5.24.3.1).

Perhaps more important (or perhaps not) is whether we include the dots in the version string.