Move profiler code from util into a new crate profile.

- Most of util::memory has been moved into profile::mem, though the
  `SizeOf` trait and related things remain in util::memory. The
  `SystemMemoryReporter` code is now in a submodule
  profile::mem::system_reporter.

- util::time has been moved entirely into profile::time.

components/net/lib.rs

@@ -26,6 +26,7 @@ extern crate png;
 #[macro_use]
 extern crate log;
 extern crate openssl;
+extern crate profile;
 extern crate "rustc-serialize" as rustc_serialize;
 extern crate util;
 extern crate stb_image;