The initial release

This is a toolbox for working with positive operator-valued measures (POVMs).
It enables users to use POVMs for sampling the state of quantum circuits (see
also povm_toolbox.sampler) and compute expectation values of any observable of
interest (see also povm_toolbox.post_processor).
The toolbox includes a library of pre-defined POVMs (see povm_toolbox.library)
which provide ready-to-go POVM circuit definitions. You can also implement your
own POVM circuits by following the provided interface.
Additionally, you can work with POVMs on a quantum-informational theoretical
footing (see povm_toolbox.quantum_info).

Starting with this release, this project will follow semantic versioning.