adding pause and resume commands

[iosefa]

I find it nice to be able to manually trigger the timer to pause and resume. To this end, we could add pause and resume commands. For example, a command flow could look like:

morning: starts the timer for the day (at the current time)
pause: pauses the timer (the beginning of a break)
resume: resumes the timer (the end of a break)
bye: stops the timer for the day (at the current time.

This can be done with the option to specify breaks as well (or automatically including them --> see #21 ).

[halsk]

@iosefa
Thank you for suggesting!

I thought it might be demanded. but I don't want to make this time tracking complicated.
I don't think we need very precisely time record.
You can adjust it by applying total (rough) break time at the end of the day.

If you want to implement it, it's welcome.
Technically, this bot is a stateless function and rely on the google spreadsheet.
You need to think about how to store the timer state.