Potentially add mruby support

[ebkalderon]

I know that mruby is not a full Ruby implementation with different goals than the others, but I think it would be nice to see its performance compared to other implementations when running compatible Ruby code. I'm hearing conflicting reports about whether mruby is actually a fast VM or not.

Thanks!

[Ravenstine]

I also came here to request this. I am even more interested in Rubinius support as well as that of Opal.

[umhan35]

It'd be nice to have mruby @brianhempel