Merge branch 'jk/fast-export-anonymize'

Sometimes users want to report a bug they experience on their
repository, but they are not at liberty to share the contents of
the repository.  "fast-export" was taught an "--anonymize" option
to replace blob contents, names of people and paths and log
messages with bland and simple strings to help them.

* jk/fast-export-anonymize:
  docs/fast-export: explain --anonymize more completely
  teach fast-export an --anonymize option