Added low freq polling mode for energy efficiency

[vnherdeiro]

Adding a mode (controlled by the --low-freq-polling flag) to calculate the time to sleep in the main loop from the time left in track:

• this aims at increasing the battery life on laptops
• it only works if you listen to a playlist without jumping tracks

Feel free to rename my variables, also a ceiling value on the sleep, to a minute ish, could be a better UX (so as to avoid hours long pocast to set a too long sleep).

[gdi3d]

Hey, thanks for the contribution but I'm not going to add it to the script.

I've already tried this a while back and there's a few use cases where this doesn't work as expected and ads get played.