Decide how to provide an authors summary on repository level.

[uliska]

As part of #12 a new tag git_authors_list has been added, but as discussed in #12 (comment) it is not clear how this really should be achieved in terms of user-facing simplicity and configurability.

The data is there and can be requested from an Author simply by not specifying a target page in Author.lines() or Author.contribution().

For now this is going to be merged as part of the Pull Request, but the question has to be fully resolved before the next release.

[timvink]

We created issues at the same time, I had created #21 slightly earlier. The outcome of that discussion would resolve this one, so closing because of duplicate.