Change author emails along with author names for pairs

[augustohp]

It would be nice to signal a pair as a different author through changing his e-mail, since that is used by GitHub to display avatars and identify authors.

We should definitely use subaddress extension of e-mails in order to do that but this poses the following problems:

1. When sorting author names (issue #3), we can't sort e-mails or we will end up with an invalid e-mail account, making the same pair to have different e-mails (depending on whose machine the pair was made).
2. Not all e-mail providers accept subaddress extension and when they accept they may not use the same separator.
3. Using initials instead of author names (issue #5) could return two different e-mail addresses for the same author.

Although none of these issues are blockers, they are problems which should be exposed and dealed in the most acceptable fashion without a configuration file being needed.