[MRG] Generate emeritus list, add dates, and change sorting

[TomDLT]

Follow up #13468 with an automatic generation of authors and emeritus tables.

• Emeritus developer list is now generated automatically.
• It also adds the dates of first and last pull-request/issue on GitHub, which is a not so bad proxy of activity. This is probably the most sensitive question.
• It also changes the order to be relative to these dates.
  Specifically:

(int(profile["first_year"]), -int(profile["last_year"]), last_name)

rendered version
rendered version

[jnothman]

i'm not sure that get_dates corresponds to the years we would consider someone to be an active core developer. But I certainly like how this looks

[NicolasHug]

Yeah, for example with myself it says I've been a coredev since 2017 while it's actually been less than a week ^^

It'd be nice also to replace <start_date> -- 2019 with <start_date> -- present

[rth]

It's nice to automate this, but at the same time not having correct dates is not ideal. Maybe removing the dates would make it less controversial?

[TomDLT]

I removed the dates.
rendered version

[rth]

Thanks @TomDLT !

[qinhanmin2014]

A new name in the emeritus list (Brian Holt)? What's happening? @TomDLT

[amueller]

Looks like I missed Brian Holt before, he should be on the list.