Pyjson5x

* Update to Unicode 15.0.0

* Fix [PEP 517](https://www.python.org/dev/peps/pep-0517/)-like installation using [build](https://github.com/pypa/build) (by [Tomasz Kłoczko](https://github.com/kloczek))

* Fallback to encode `vars(obj)` if `obj` is not stringifyable, e.g. to serialize [dataclasses](https://docs.python.org/3/library/dataclasses.html)
* Update documentation to use newer [sphinx](https://www.sphinx-doc.org/) version
* Use [dependabot](https://github.com/dependabot) to keep dependencies current
* Update [fast_double_parser](https://github.com/lemire/fast_double_parser)

* Add [PEP 484](https://www.python.org/dev/peps/pep-0484/) type hints (by [Pascal Corpet](https://github.com/pcorpet))
* Update [JSONTestSuite](https://github.com/nst/JSONTestSuite)

* Add file extensions to fix compilation with current Apple SDKs
* Update fast_double_parser to v0.5.0
* Update to Unicode 14.0.0d18

* Update up Unicode 14.0.0d9