Iteration-utilities

- Source distribution now includes all files needed to run the tests from the tarball

- Improve performance of ``ipartition`` by evaluating the predicate only once
per item.

- Add benchmarks comparing some functions with other libraries.

- Python 3.12 compatibility

- Dropped Python 3.5 and 3.6 compatibility

- The top level ``__version__`` property was removed. ``importlib.metadata.version`` from the
Python standard library should be used if you need the version of ``iteration_utilities``.

------

- The functions implemented in C now parse boolean arguments based on their
truth value instead of their integer value. This should be unnoticeable in
typical usage.

- Added ``always_iterable`` which wraps non-iterable inputs with an iterable.

- Added ``empty`` as singleton representing an empty iterable.

- The type of ``Placeholder`` which was previously accessible as
``PlaceholderType`` private.

- Added Python 3.9 support.

Fixed some reference counting bugs in merge, sideeffects, and minmax

- Exception message for one if the iterable contains more than one element does show the first two elements.
- Fixed a bug in grouper that lead to a fatal exception.

Dropped support for Python <= 3.4 including Python 2.7.

Add a new recipe from the itertools documentation: nth_combination.

Added a few new functions that rely on new functions in the Python statistics module:

- Iterable.get_fmean (Python >= 3.8)
- Iterable.get_geometric_mean (Python >= 3.8)
- Iterable.get_harmonic_mean (Python >= 3.6)
- Iterable.get_multimode (Python >= 3.8)
- Iterable.get_quantiles (Python >= 3.8)