git-fame v1.8.0 stable

• add --cost=<method> (#16 -> #18)
  • COCOMO|months (person-months)
    • https://en.wikipedia.org/wiki/COCOMO
  • commits|hours (person-hours)
    • https://github.com/kimmobrunfeldt/git-hours/blob/8aaeee237cb9d9028e7a2592a25ad8468b1f45e4/index.js#L114-L143
• update bash completions
• replace default built-in backend with tabulate
• add and update documentation
  • update man pages
  • mention .mailmap to fix https://www.mistergoodcat.com/post/analyze-your-git-repositories
  • fix badges
  • update DOI
• tidy and lint (flake8)
• add and update unit tests
  • fix PyYAML tests for latest pyyaml>=5