Fixedpoint

* Added changelog.
* Added py.typed into release files per [PEP 561][] so
[mypy](https://mypy.readthedocs.io/en/stable/installed_packages.htmlmaking-pep-561-compatible-packages)
will recognize fixedpoint as a typed package.
* Added py.typed into [fixedpoint](/fixedpoint/) directory
* Added py.typed as package_data in [setup.cfg](/setup.cfg).
* Added installation instructions in the documentation.

* Initial release.

[Keep a Changelog]: https://keepachangelog.com/en/1.0.0/
[Semantic Versioning]: https://semver.org/spec/v2.0.0.html
[PEP 440]: https://www.python.org/dev/peps/pep-0440/
[PEP 561]: https://www.python.org/dev/peps/pep-0561/