Add missing __init__.py file
Fix setup.cfg

Trailing whitespace and typo.
Expose VersionInfo from oslo.version package
Use properties for various version strings

No need to expose the weirdness of attributes which need to be
initialized by calling foo_string() methods.
Remove some old weird methods

Definitely no need to retain "compatibility methods". Let's just fix
the code which uses the old names.

cached_version_string() doesn't seem to do anything useful anymore
either.