[feature] Use a same key to toggle pomodoro

[Freed-Wu]

set -g @pomodoro_start C-a
set -g @pomodoro_cancel C-a

It cannot work. How about:

set -g @pomodoro_toggle C-a

? Thank you.

[olimorris]

Sorry for the delay in replying to this. A great suggestion and I've implemented this in 0002365c2b7fa2842a0dbfabe906faad40d6c9dc.

I didn't want to break mappings for everyone so I've kept the API the same.