Removed dependency on category-extras.
Removed dependency on category-extras.

It was becoming annoying because of duplicate package
names - category-extras and control-monad-free fighting
for Control.Monad.Free - so I just copied the stuff I
need from category-extras (the Pointer comonad into here).

pepeiborra/narradar,pepeiborra/narradar,pepeiborra/narradar