Macro embedded_builder::field_trait

macro_rules! field_trait {
    (r, $name: ident, $field: tt, $t:ty, $shift: expr) => { ... };
    (w, $name: ident, $field: tt, $t:ty, $shift: expr) => { ... };
    (r, $name: ident, $field:tt, $t:ty, $shift:expr, $mask:expr) => { ... };
    (w, $name: ident, $field:tt, $t:ty, $shift:expr, $mask:expr) => { ... };
}