Tracking possible breaking changes

[cuviper]

Since num is widely used, we should only sparingly bump semver, but when we do we should batch breaking changes together.

This is a place to track changes that we might make. These may be API changes that would break existing users, of course, but also changes that would require us to increase the minimum Rust version. Inclusion on this list does not guarantee we will do it, and exclusion probably just means it wasn't considered yet. (If the need arises, we can also explicitly list changes we won't make.)

Proposed breaking changes

• Hide bigint implementation details #155 Hide bigint implementation details, basically removing BigDigit from the public interface.
• std::num::Checked{Add,Sub,Mul,Div} should have type parameters #59 Add type parameters to Checked traits.
• All bit twiddling functions in num::traits::PrimInt should take or return usize instead of u32 #80 Change PrimInt shifting bounds from RHS=usize to u32, for consistency with its methods.
• next_after for Float #118 next_after for Float (still unstable!)
• Summing Vec<Complex<T>>: difference between core::num::Zero and num::traits::Zero #126 Use/extend std versions of Zero and One (still unstable!)
• Improve pow speed for expensive types by multiplying references not cloned values (reopen) #153 Use Mul by reference in num::pow.

[cuviper]

Is this tracker actually useful? I don't really like that GitHub doesn't show any change history when I edit the list. Maybe we should just have a breaking-change label instead.

[hauleth]

I think labels is good idea.

[cuviper]

Alright, the issues above have labels now.