Thejoker

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- Fix bug with ``plot_phase_fold()`` that would cause it to fail if ``data=None``.
- Overhaul packaging layout to use more modern practices.
- Replace the ``pymc3`` backend to use the newer ``pymc``.

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- Fix bug with wheel builds.

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- Compatibility with astropy v5.0 and python 3.10.

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- ``TheJoker`` now expects a ``numpy.random.Generator`` instance instead of a
``RandomState`` for controlling random number generation.

- Renamed ``t0`` to ``t_ref`` in places where it actually represents a reference
time.

- Added functionality to compute ``t0``, i.e. the time of phase=0, for samples.

- Added functions to compute time-sampling statistics for the samples returned
from The Joker (see: ``thejoker.samples_analysis``).

- Fixed a bug in the ``UniformLog`` distribution that affected running MCMC.

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- Removed ``astropy-helpers`` from the package infrastructure.
- Switched to using ``tox`` for testing and documentation builds.
- Fixed bug in ``JokerSamples.read()`` when reading from an HDF5 file.