[feature request] Remove `Copy` bound from `Real`

[CraftSpider]

Basically the reverse request of #243 - Currently, Real implies Copy, which restricts it from being implemented for real-value types that use non-copy internals (for example, a type that represents values as whole fractions backed by a BigInt). The Copy bound doesn't seem to be actually useful to the trait, and more like a holdover from when it was split out from Float.

This would be a breaking change unfortunately.

[CraftSpider]

Just an added thought - If this change is made, it may be a good time to add Bounded as a super-trait and remove the min_value and max_value methods, as they're documented to do the same things