Finish making submodule releases possible.

[aiuto]

• fix a lot of bugs in release_module.yaml and release_prep.sh
• update the version.bzl file for the submodule when releasing. That's one less thing to be out of sync.
• update pkg/releasing tools to allow for releases that are not strictly a version number.

This was used to create the release rules_pkg_providers-0.0.1g.
After this is committed, I'll delete that pre-release sample and do a real one.