Merge: contrib: Introduce nitrpg

We have been talking about this a long ago. I made some demos, merged the full Github API stack...

Tonight is the nigth!

In this first PR we introduce some game basics and just enough to show how the game is supposed to work.
You can run it as this but the game only rewards new pull requests and +1 comments.
Further PR will introduce more capabilities like Github history reload, achievements, experience...

The game is separated into two tools:

* `listener` is the Github hook that capture all the github events on a repo.
* `web` is a Nitcorn client that display the game as a HTML website.

Four first commits are from #1141, please disregard.

Pull-Request: #1142
Reviewed-by: Jean Privat <jean@pryen.org>
Reviewed-by: Lucas Bajolet <r4pass@hotmail.com>