Provide ability to create getters that return `A<&T>` instead of `&A<T>`

[alopatindev]

Thanks for this awesome crate!

#[derive(Default, getset::Getters)]
struct A {
    #[get = "pub"]
    b: Option<B>,
}

#[derive(Default)]
struct B;

fn main() {
    let a = A::default();
    let b: Option<&B> = a.b();
}

error[E0308]: mismatched types
  --> src/main.rs:12:25
   |
12 |     let b: Option<&B> = a.b();
   |            ----------   ^^^^^
   |            |            |
   |            |            expected enum `Option`, found `&Option<B>`
   |            |            help: you can convert from `&Option<T>` to `Option<&T>` using `.as_ref()`: `a.b().as_ref()`
   |            expected due to this
   |
   = note:   expected enum `Option<&B>`
           found reference `&Option<B>`

Getters that return &Option<T> (just like &Result<T>, etc.) are not really useful, as they require getter user to pollute code with .as_ref() everywhere. As alternative, having manual trivial getters like

impl A {
    pub fn b(&self) -> Option<&B> {
        self.b.as_ref()
    }
}

is just another kind of boilerplate code pollution.

Can we do anything with this (and not some breaking change at the same time of course)?

I guess solution would likely require working with each such type separately (perhaps adding OptionGetters and #[get_option = "pub"], etc.), but still this would make this crate more coherent for users.

[mversic]

I'd be happy to implement this as the default for Option<T> and/or Result<T, E>. Additionally, I would implement Vec<T> -> &[T], String -> &str. I cannot think of a reason why this would be preferred. This would be a breaking change though