Change syntax extension syntax: #m[...] -> m!{...}.

src/libcore/future.rs

@@ -7,7 +7,7 @@
  * ~~~
  * let delayed_fib = future::spawn {|| fib(5000) };
  * make_a_sandwich();
- * io::println(#fmt("fib(5000) = %?", delayed_fib.get()))
+ * io::println(fmt!{"fib(5000) = %?", delayed_fib.get()})
  * ~~~
  */