A Procedural Macro for Decorators

The Decorator macro generates a decorator method for each field, which is marked with #[dec] in front. Additionaly a field of type Option<T> can be marked with #[opt_dec]. This generates a decorator method that will set the value to Some(t).

Example

```rust

[derive(Decorator)]

struct Widget { #[dec] width: u32, #[dec] height: u32,

#[opt_dec]
background_color: Option<RGBA>,

} Generates into: rust struct Widget { width: u32, height: u32, backgroundcolor: Option, } impl Widget { pub fn width(self, width: u32) -> Self { Self { width, ..self } } pub fn height(self, height: u32) -> Self { Self { height, ..self } } pub fn backgroundcolor(self, backgroundcolor: RGBA) -> Self { Self { backgroundcolor: Some(backgroundcolor), ..self } } } Which can be used like: rust let w = somewidget.width(10).height(20); asserteq!(w, Widget {width: 10, height: 20, backgroundcolor: None}); ```