Cppyythonizations

**Changed:**

* Changed packaging to use pyproject.toml instead of the overly complicated autotools setup copied over from the C++/Python projects.

**Fixed:**

* Adapted cppyythonizations to different ways of type printing in different versions of cppyy.
* Include tribool in the distributed package.

**Fixed:**

* Do not break inplace operators in `enable_arithmetic`.

**Fixed:**

* Fixed typo in `make uninstall` command.
* Include `MANIFEST.in` in distributed cppyythonizations tarball.

**Added:**

* Added `cppyythonizations.boost.type_erasure` to make methods on erased types available in cppyy.

**Fixed:**

* Removed explicit cancel workflow for GitHub CI (replaced by newer builtin feature.)
* Allow installation of cppyythonizations with `pip install -e`.

**Added:**

* add package to PyPI so we can `pip install cppyythonizations`

**Fixed:**

* adapt serialization to changes in cppyy 1.9.0
* only run GitHub workflows once for master but not for pushes to tags.