Support defining a mapping between author identifier and the author in the feed

[stefansli]

The RSS standard specifies the author should be [email protected] (John Doe). In the documents I'd like to use a username, for example the github username, as author. Would it be possible to implement a mapping between usernames and RSS authors?
I'm thinking aboud a new config setting and a yaml file that maps the authors to RSS Name + Email definitions.
Alternatively one could implement rss_author and rss_authors metadata.

Background information:
I'm using the mkdocs-material theme with the blog plugin. The blog plugin can also render pages for authors. With the current setup, specifying a RSS conform author, the URL to the authors page looks quite ugly (containing %40 for the @ and several spaces).

Do you thinkt that's a good idea? Then I'd start with an implememtation and open a pull request.