--took option for done and finish, basic command line command result output

Sets the completion date to an interval from the start date. Specified with "HH:MM" or "2h20m," or just "15m" or "1.5h".

In combination with the --back flag on `done`, you can set a date in the past and finish it with proper time tracking without doing _math_. `doing done --back "yesterday noon" --took 1.5h did that thing...`

Functions can store front-facing messages in @results (Array). All messages are output after the command runs.

Signed-off-by: Brett Terpstra <me@brettterpstra.com>