feat(macros): add sub mul div zero derives

[milancermak]

Pull Request type

Please check the type of change your PR introduces:

• Bugfix
• Feature
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no API changes)
• Build-related changes
• Documentation content changes
• Other (please describe):

What is the new behavior?

PR introduces a bunch of new macros that allow to derive Add, Sub, Mul, Div, AddAssign, SubAssign, MulAssign, DivAssign and Zero traits. Now we can have a struct like this:

#[derive(Add, AddAssign, Sub, SubAssign, Mul, MulAssign, Div, DivAssign, Zero)]
struct Foo {
    x: u8,
    y: u16,
    z: u32
}

and all the basic ops are available out of the box.

The macros work for more complex types as well (generic & nested structs).

Does this introduce a breaking change?

• Yes
• No

Other information

I've cleaned up the package structure to be more modular as it grows.

[enitrat]

awesome!