Atomic operations module. All the atomic_* intrinsics are inc...

All the atomic_* intrinsics are included, but only CAS is wrapped.
If desired, the wrappers for all the operations can copied from [the implementation in libstd](https://github.com/mozilla/rust/blob/master/src/libstd/unstable/atomics.rs#L346-L516).
The type wrappers are nice, but not as useful right now (feel free to contradict me).