Implement remainder operator

[tertsdiepraam]

We have +, -, * and /, but no % for modulo/remainder. We should probably add that!

• We do have to decide what to do with negative values. E.g. is -5 % 3 equal to -2 or 1. Rust does -2 and Python says 1. The operation returning 1 is instead called rem_euclid in Rust.
• The % must have the same precedence as the * and / operators.

I think this could be implemented as a good first issue, because it's mostly looking at what happens with the other operators, but it's not trivial.

[LevitatingBusinessMan]

We do have to decide what to do with negative values. E.g. is -5 % 3 equal to -2 or 1. Rust does -2 and Python says 1. The operation returning 1 is instead called rem_euclid in Rust.

Ruby says 1, JavaScript says -2, C says -2.