Merge: Nitrpg: add achievements

Not much achievements in this PR:

* Counting issues and rewarding at 1, 100, 1000
* Counting PR and rewarding at 1, 100, 1000
* Counting commits and rewarding at 1, 100, 1000, 10000
* Two achievements based on regexp, just for demo: Nitdoc and FFI

Partially fixes #1165: I fixed the typo in "complaint" and the first playre to unlock the achievement. But the related issue stills not linked for now.

Démo: http://nitlanguage.org/rpg/games/privat/nit (sorry, I had to reset the scores...)

Pull-Request: #1171
Reviewed-by: Jean Privat <jean@pryen.org>
Reviewed-by: Lucas Bajolet <r4pass@hotmail.com>