Make Int % Uint return a Uint

[andrewwhitehead]

Fixes #847

The result of taking a signed integer modulo an unsigned one should be unsigned. Python agrees at least:

>>> hex(-0x112709385A4E59AFCE14364856CB6D1760D7D2B618A2DA9F85A96C4C2751D179 % 0xde157f812521c55eccf9a903b31e4a34)
'0x44bfe3176459710d0d0848f99b37e47b'
>>> hex(0x112709385A4E59AFCE14364856CB6D1760D7D2B618A2DA9F85A96C4C2751D179 % 0xde157f812521c55eccf9a903b31e4a34)
'0x99559c69c0c85451bff1600a17e665b9'

This also removes the RemAssign implementations, Int %= Uint. If somebody needs to do this, I think they can do a checked conversion to an Int for the modulus first.

[fjarri]

I think in Rust's terms that makes it rem_euclid rather than rem.

[andrewwhitehead]

I think in Rust's terms that makes it rem_euclid rather than rem.

Yes, it's also possible to rename these methods to rem_euclid and add a separate RemEuclid trait. A checked_rem method that returned a CtOption<Int<LIMBS>> would also be possible (checking if the modulus fits in an Int).