Trying to get more sensible defaults for people who like to think about
graphstates rather than circuits.

Repsponse to issue #4: [Link](https://github.com/peteshadbolt/abp/issues/4)

- `GraphState.copy()`
- `measure_x` etc.
- `measure(detail=True)`
- Better documentation on `remove_vop` and `act_local_rotation`