Initial version description
Add classdoc
Add ref,hash,repo to Version
Add has_version
Be consistent with assertions
More pythonic has_hex
Move test_version
JSON deserialization

Will parse first argument as json version object.

TODO: More error handling.
Only add known fields and verify version validity
Add equality
Merge branch 'feature/repo-versions'

Conflicts:
	src/git/version.py
	tests/git/test_repository.py
	tests/git/test_version.py