Added Pocket support

Saw this script set mentioned somewhere this afternoon but was disappointed that it didn't support Pocket (my read-it-later service of choice right now). I looked around and didn't find a whole lot of options for Pocket API support in Python so I wrote my own, based on the InstapaperLib script. The authentication is tweaked to work with Pocket's OAuth scheme.

Tonight was the first time I've ever written in Python and I know my code could definitely be improved; I'm hoping that contributing this (which does work) might prove a useful starting point to getting better code written.