create Git release commits and tags with changelogs

 git-bump automates the best practices for doing releases for
 code bases stored in Git:
 .
  * Update version-related minutiae in the code base.
  * Commit with a message like projectname 1.2.3.
  * Create a signed, annotated tag with the same message with a name like
    v1.2.3.
  * Include release notes in the release commit.