Prepare release 0.23.0

Fix typo in changelog

Add release 0.22.2

Return to old implementation of `TopologicalSort`

Add TopologicalSort disclaimer to CN README

Fix typo in BFSWithDepth GoDoc

Add graph v0.20 logo (#115)

Change release date of graph 0.19.0

Implement `Union` for combining two graphs into one (#100)

Remove gofumpt (#98)