grcov coverage support

[sagiegurari]

Features Description
Add coverage provider tasks for grcov

[sagiegurari]

I think this one should be implemented after mozilla/grcov#326 is handled instead of building an entire flow inside cargo-make makefile.

[kazuk]

I write cargo-make makefile for grcov.

https://github.com/kazuk/cargo-make-coverage-grcov

this works on my box (Ubuntu 20.04)

[sagiegurari]

really cool. i'll try it out soon.

[sagiegurari]

Thanks, this is really great. I'll update the readme to reference your repo.