Explicitly bind trait methods

[Nadrieril]

We should make explicit the mapping between trait parameters and method parameters, like I explained here:

trait Trait<T> {
    fn method<U>();
}
impl<T> Trait<Foo<T>> for Bar<T> {
    fn method<U>() {}
}
// represented as:
fn impl#0::method<T, U>() {}
impl<T> Trait<Foo<T>> for Bar<T> {
    fn method = for<U> impl#0::method<T, U>
}

This will unlock #180 and #127.