Adding number of pomodoros option.

Hi,

First of all, I would like to congratulate everyone involved with
tomighty, this is not just useful but also very well crafted, I had no
problem reading the code.

This feature I'm trying to but together is described on issue #79, not
sure if this pull request contemplate what the users had in mind so I
decided to show this initial work.

I would like to ask for feedback not only on the feature (if it's good
for the users) but also in the code I have written.

Cheers.