Update stage0 bootstrap compiler

We've got a freshly minted beta compiler, let's update to use that on nightly!
This has a few other changes associated with it as well

* A bump to the rustc version number (to 1.19.0)
* Movement of the `cargo` and `rls` submodules to their "proper" location in
  `src/tools/{cargo,rls}`. Now that Cargo workspaces support the `exclude`
  option this can work.
* Updates of the `cargo` and `rls` submodules to their master branches.
* Tweak to the `src/stage0.txt` format to be more amenable for Cargo version
  numbers. On the beta channel Cargo will bootstrap from a different version
  than rustc (e.g. the version numbers are different), so we need different
  configuration for this.
* Addition of `dev` as a readable key in the `src/stage0.txt` format. If present
  then stage0 compilers are downloaded from `dev-static.rust-lang.org` instead
  of `static.rust-lang.org`. This is added to accomodate our updated release
  process with Travis and AppVeyor.

src/liballoc/lib.rs

@@ -87,7 +87,6 @@
 #![feature(needs_allocator)]
 #![feature(optin_builtin_traits)]
 #![feature(placement_in_syntax)]
-#![cfg_attr(stage0, feature(pub_restricted))]
 #![feature(shared)]
 #![feature(staged_api)]
 #![feature(unboxed_closures)]