Optionally add # time as duration

[runarberg]

Sometimes I write my test outputs to .tap files and run the formatter as a separate process. In that case I would like to be able to end the file with an indicator for the time duration. For example:

1..42
# tests 42
# pass 40
# fail 2
# time 1024

It would be nice if the test duration could be written straight to the TAP output and that the spec formatter would listen to that when present instead of measuring its own time.

  assertions:  42
  passing:     40
  failing:     2
  duration:    1s