v0.20

Changes

• Enable support for pattern matching (#96)
  (by @antonagestam in 7071a24)

• add support for aix/sunos (#98)
  (by @mattp- in 765e4ee)

• Python 3.12 compatibility (#105)
  (by @elprans in f797822)

• Add contains to MapKeys (#99)
  (by @msullivan in 6790111)

• Add PEP 585 GenericAlias support (#101)
  (by @eltoder in 9ce64c5)

• Move metadata to pyproject.toml, fix test fixture inclusion in sdist (#111)
  (by @elprans in ea65656 for)