- Use AtomicInterface to implement device-specific atomic operations.
- Remove DeviceAdapterAtomicArrayImplementations.
- Extend supported atomic types to include unsigned 32/64-bit ints.
- Add a static_assert to check that AtomicArray type is supported.
- Add documentation for AtomicArrayExecutionObject, including a CAS
  example.
- Add a `T Get(idx)` method to AtomicArrayExecutionObject that does
  an atomic load, and update existing CAS usage to use this instead
  of `Add(idx, 0)`.