294 continue xp algebra (#304)

* Modify antisymmetric_op based on Issue 299 and change use of compose in tests

* Add inverse method (to base_xp_pauli, xp_pauli, and xp_pauli_list) and tests

* Add conjugate method and tests

* Add commutator method and tests

* Add fundamental_phase method and tests

Also modify power method such that each operator in an XPPauliList can be raised to different powers

* Add reset_eigenvalue method and tests

* Linting cleanup

* Fix small error in reset_eigenvalue method

* Add "See also" in docstrings

* Modify `power` based on comments

The `power` method now accepts int, list, or np.ndarray as input. If an int is provided, all XP operators in an XPPauliList would be raised to the same power.

* Revert change in precision check

* Add docstrings for x, _x, z, _z

* Add warnings and inplace option for `rescale_precision()`

* Add inplace option for `reset_eigenvalue()`