Request new command: alr mrproper

[pmunts]

alr mrproper would be exactly equivalent to rm -rf alire bin config obj share, and removes everything that is or can be regenerated automatically. It is also equivalent to make mrproper and
make distclean as are commonly used in make projects.

What remains after alr mrproper is the minimal portion of an Alire project that is suitable for checking into a source code repository.

Adding a new option like --mrproper or --pristine or even --all to alr clean would be equivalent.

[Fabien-Chouteau]

I think a --distclean option for alr clean is the best way. We don't need a new command for that.

[jquorning]

note: In brew package manager for Ruby1 we use doctor2 for cleaning up the package library and setup.