Macro melib::_impl

macro_rules! _impl {
    ($(#[$outer:meta])*$field:ident : $t:ty) => { ... };
    (get_mut $(#[$outer:meta])*$method:ident, $field:ident : $t:ty) => { ... };
    (get $(#[$outer:meta])*$method:ident, $field:ident : $t:ty) => { ... };
}