Include version-tuple and/or packaging.version versions of the various package-level version constants

[CAM-Gerlach]

As originally discussed on #414, it might be nice to be able to actually check the version, though for that we really should do a proper version comparison on the QT_VERSION (for which it would be a good idea to parse it and the other versions in __init__ to "version_info"-style version tuples, e.g. under QT_VERSION_INFO and similar, and/or packaging.version objects (since packaging is already a dependency and which can be compared and indexed like tuples, but also handle a much wider variety of version syntax correctly and have a number of additional useful features, which might be more generally useful to users and ourselves than just raw strings.