Refactor AUTHORS file to make it easier to add new AUTHORS with each release

[misterdjules]

The current AUTHORS file is ordered by time of first contribution to the project, and there is actually no way to automatically get rid of duplicated entries for the same author with different email addresses.

The release tools should generate an AUTHORS file ordered alphabetically by authors' names and should generate a .mailmap file that maps authors' names to email addresses.

[misterdjules]

Fixed by 31610d0, which actually doesn't generate a .mailmap file automatically. It was implemented, but it turns out that it's easy to automatically add bogus entries to it.