Three new metrics:
* number of errors (boo)
* number of warnings (and advices)
* percentage of documentation (with ponderation)
The 3 firsts commits was to make errors&warnings accessible without printing them.
Pull-Request: #2081
Reviewed-by: Alexandre Terrasa <alexandre@moz-code.org>
Reviewed-by: Lucas Bajolet <r4pass@hotmail.com>