Setuptools-cythonize

- Bugfix/incompatibility with setuptools 63.4.0 (8)

* Add MANIFEST.in and include license file in src distribution
* Don't set a default compiler on Windows

* Only files `__init__.py` and `__main__.py` are excluded from the cythonization
* Cython compiler options are no more set by `setuptools_cythonize` (`embed_pos_in_docstring`, `fast_fail` are now `False` by default)
* Fix command `python setup.py install` (however, the package will not be installed as an eggs)

* Fix minor mistakes in README
* Add directive to ensure cython compiles in the correct python version

Documentation update