Implement the provided operators for Rgb manually

[nickelc]

This removes the overload dependency by implementing the operators for the Rgb struct manually.

The overload macro is a bit opaque about what it generates without looking into the documentation. The generate code is fairly simple and therefore I think it's reasonable to maintain the implementation here.

[sholderbach]

I am generally on board with trying to keep the depency footprint as small as possible

In this case the effect on build times is neglible as the overload crate is entirely build with macro_rules! macros instead of being a proc macro crate where the proc_macro2/quote/syn compile chain has a big impact.

Output from cargo clean && cargo build --timings:

[nickelc]

I'm aware that it's just a macro_rules! and that the build times are negligible.

I saw new transient dependencies popping up in my project, checked them out and
wouldn't mind if the macro was used for more than one type.

[fdncred]

+1 for readability

[sholderbach]

I'm on board with keeping it straightforward over saving a few lines of boilerplate.

Thanks for taking up the chores!