- Adds `Collection` classes for easily working on collections of distributions in a similar manner to a single distribution.
- Adds the ability to pass `expval` functions a string of operators, eg. `'IZZZIZII'`, that indicate which diagonal operator is assumed to act on the given qubits.
- Adds tutorials section to documentation.
- Adds new basic VQE tutorial to show how one can use mitigation in a simple iterative algorithm.