Remove Author.email field and merge authors by name

For example `John Smith <john.smith@example.com>` and `John Smith <jsmith@example.com>` are considered as a single author `John Smith` regardless of the different email addresses.

As the URL for author details is constructed from `Autor.dirname` (as opposed to `Author.email` - see dc4d2a0) the original version does not work properly.

This change is just a workaround and is not intended for a direct merge, I created it just to trigger a discussion.

However, for me personally it feels as a suitable quickfix until the whole issue is properly addressed.