RfE: Unify GitAuthors over many .git repositories

[ascheman]

This is a request for enhancement. When scanning multiple .git repositories authors should be unified: If the same person (identified by his full name including mail address) is contributing to many projects she should still be treated as the same entity. Currently each .git repository creates its own set of authors.

Independently we could think about unifying GitAuthor objects even if they use different full names and mail addresses over time or for different repositories. This, however, seems to need a configuration somehow.