Merge branch 'es/contacts'

A helper to read from a set of format-patch output files or a range
of commits and find those who may have insights to the code that
the changes touch by running a series of "git blame" commands.

* es/contacts:
  contrib: contacts: add documentation
  contrib: contacts: add mailmap support
  contrib: contacts: interpret committish akin to format-patch
  contrib: contacts: add ability to parse from committish
  contrib: add git-contacts helper