Feature request: ability to profile commands

[fatkodima]

Currently, CLI is able to profile only single ruby files via memory-profiler ruby_file.rb (we pass a file name and the gem loads it and profiles the memory).
It will be very convenient to be able to profile whole commands/processes, like rspec, rails etc via something like
memory-profiler run ...gem options... -- rails test ...command options....

The interface will like the one added for stackprof (tmm1/stackprof#187).

If this is OK, I can open a PR.

[SamSaffron]

seems fine to me , sure give it a shot