* Add source_url_pattern to be able to use the "link to source" button
* Add README.md as an "extra" where it wasn't already
* Add a `main` setting. They all have a very obvious main module. Set
that as `main`, so a user is shown this immediately instead of a list
of usually only this module.
Bryan Naegele
Patrik Stenmark
Maarten van Vliet