Output feedback text

*Thank you for making/maintaining `tasklib`!*

Per https://taskwarrior.org/docs/hooks.html (my emphasis):

> Output from a hook script is a combination of a JSON-formatted task and text. Just as the JSON for a task must occupy a single line, so must a single feedback message. Feedback text is optional for a successful hook script, but **required** for a failing script. If provided it will be displayed by Taskwarrior according to the verbosity setting.
>
> Here is sample output from a hypothetical spell-checking hook script:
>
> {"description":"Buy some milk","entry":"20141118T050231Z","status":"pending","uuid":"a360fc44-315c-4366-b70c-ea7e7520b749"}
> Spell checking found no errors.
>
> The output is a single line JSON object which represents an optionally modified task, and a single line of feedback text to be displayed.
>
> There may only be one line of JSON, and it must be for the same task that was provided as input.

However, `tasklib` does not seem to have a (documented) way to output feedback text.