phase: use a better name on output

By defaut this uses the lowercased prefix of the classname.
But specific phases can redefine `to_s` if required.

Signed-off-by: Jean Privat <jean@pryen.org>
phase: add option --disable-phase

Can be used to desactivate specific phases when testing and debugging.
The option can also lists the sequence of phases and their dependencies.

Signed-off-by: Jean Privat <jean@pryen.org>
Merge: Opt disable phase

`--disable-phase` to disable phase and broke tools :)

The point is to improve testing and comparison with and without specific (optional) phases

Pull-Request: #371
Reviewed-by: Lucas Bajolet <r4pass@hotmail.com>