Have floating point functions take their parameters by value.

Have floating point functions take their parameters by value.

Make all of the methods in `std::num::Float` take `self` and their other parameters by value.

Some of the `Float` methods took their parameters by value, and others took them by reference. This standardises them to one convention. The `Float` trait is intended for the built in IEEE 754 numbers only so we don't have to worry about the trait serving types of larger sizes.

[breaking-change]