Add a cross-RFC relations section within RFC

When I was reading RFC https://github.com/rust-lang/rfcs/blob/master/text/0320-nonzeroing-dynamic-drop.md, then I came across the code segment:

#[deriving(Show)]
struct AnnounceDrop { name: &'static str }

impl Drop for AnnounceDrop {
    fn drop(&mut self) { println!("dropping {}", self.name); }
}

fn foo<A>(a: [A, ..3], i: uint) -> A {
    a[i]
}

fn main() {
    let a = [AnnounceDrop { name: "fst" },
             AnnounceDrop { name: "snd" },
             AnnounceDrop { name: "thd" }];
    let r = foo(a, 1);
    println!("foo returned {}", r);
}

where I was interested to see how rustc will handle it, as expected, this code does not compile today:

error[E0508]: cannot move out of type `[A; 3]`, a non-copy array
  --> /tmp/test.rs:13:5
   |
13 |     a[i]
   |     ^^^^ cannot move out of here

error: aborting due to previous error

Then I realize there must be an RFC that alter the semantics of the compiler, which I think is https://github.com/nox/rust-rfcs/blob/master/text/0533-no-array-elem-moves.md

Here comes a problem, as RFCs grows in numbers, how could a new comer follow the changes of Rust and have a good view of the current state?

I guess adding a section where it states what newer RFCs have fully/partially obsolete what part of this RFC would be a great help to follow the evolution of Rust.