Release type: minor

* Modernize and improve tests ([#32](https://github.com/getpelican/feedgenerator/pull/32) & [#34](https://github.com/getpelican/feedgenerator/pull/34) — thanks to @venthur)
* Drop support for Python 3.6 and test on 3.10 & 3.11 ([#35](https://github.com/getpelican/feedgenerator/pull/35) — thanks to @hugovk)
* Exclude `tests_feedgenerator/__pycache__` from distribution ([#33](https://github.com/getpelican/feedgenerator/pull/33) — thanks to @BenSturmfels)