Added a plugin for searching The Pirate Bay

I tweaked an existing plugin to create a new one that searches The
Pirate Bay using “pb” as the identifying search initiator.

This is my first plugin (I just recently started programming) and my
first time using GitHub, so I apologize in advance for being a noob :-)
Merge pull request #122 from nicklaslind/master

Added a plugin for searching The Pirate Bay