Add changelog entry for 0.22.1

Start development of 0.23

Fix import of Literal

Start development of 0.22

Minor changelog typo.

Prepare 0.20.1 release.

Start development of 0.21

Move up deprecations in CHANGELOG.

Deprecations are generally important information and should be read
first.

Start development of 0.20

Merge branch 'master' of github.com:bpython/bpython