Adding a newtype EndoCategory to Control.Category (ticket #3362)

I suggest adding a wrapper to make (a x x) a Monoid for any Category a and type x. This would be added to Control.Category. newtype EndoCategory a x = EndoCategory { runEndoCategory :: a x x } instance (Category a) => Monoid (EndoCategory a x) where mempty = EndoCategory id mappend (EndoCategory f) (EndoCategory g) = EndoCategory (f . g) -- Russell O'Connor http://r6.ca/ ``All talk about `theft,''' the general counsel of the American Graphophone Company wrote, ``is the merest claptrap, for there exists no property in ideas musical, literary or artistic, except as defined by statute.''