[[!comment format=mdwn
 username="joey"
 subject="""comment 7"""
 date="2018-02-19T19:49:11Z"
 content="""
Basic --json-error-messages implemented after 4 hours work.

Still needing to be done:

* A few commands like `git annex info` have a custom json outputter,
  and may not output the error-messages field by default, or may not make
  sense to support the option.
* Flush json buffer after fatal error.
"""]]
