A logfmt formatter backend for the Elixir console logger backend, tailored to Logbook needs.

Ideally it should be used with the metadata: :all option of the console backend.

The log line is made of the following keys:

• date: date of the entry, in YYYY-MM-DD format.
• time: time of the event, in hh:mm:ss.msec.
• level: the log level.
• msg: the actual log message.
• tag: Logbook specific: comma separated list of logbook tags, fallbacks to

     `default` if the log entry has no tags.

• module: module emitting the log.
• function: function emitting the log, in the form function/arity.
• vm_pid: OS pid of the erlang vm.
• host: hostname of the system, as returned from :inet.gethostname/0.

Remainig metadata is appended to this list. Note that the :mfa key is dropped since module and function are already reported.