Simplify numeric traits

[brson]

Tracking rust-lang/rfcs#369

[brendanzab]

I updated the issue description to point to the correct RFC.

[brendanzab]

By the way, I would love to work on implementing this. I will have a great deal more time on my hands after my last exam tomorrow.

[ogham]

Is there a reason that the Int and Float traits need to implement Copy? I started writing an interface to the MPFR library, but its types need to implement Drop, which means they can't be copied... it's a shame, because it's otherwise a perfect with for Float and FloatMath.

[alexcrichton]

This has been implemented for some time now, co closing.