Release 1.8.3

Add per-artifact multi-module publish/consume

ArtifactEntry gains a 'modules' flag: an artifact { modules = true } entry
expands to one release asset per subproject (<repo>-<module>.jar), and can
be combined with regular classified jars in the same release.

Consumers pull a single module via the classifier (owner:repo:tag:module)
or the whole library at once via the reserved 'all' classifier
(owner:repo:tag:all), backed by GitHub.getAllModuleAssets.