procedural macro on struct, auto implement fn from_element

[diegodox]

[Feature Request] Implement procedural macro FromElement on struct, auto implement fn from_element that enable us to do below

#[derive(ply::FromElement)]
struct ElementStruct {
    x: f64,
    y: f32,
    z: u8
}

then

let elements: Vec<ElementStruct> = ElementStruct::from_element(element).unwrap().collect();