move GArrow from GHC.HetMet to Control
comment out references to module not implemented yet
GArrowFullyEnriched: minimize context of the data declaration
GArrowFullyEnriched: clean up imports and context
GArrowFullyEnriched: avoid need for UndecidableInstances
GArrowFullyEnriched: better algorithm, avoids drop/copy/swap
rename GArrowKappa to GArrowFullyEnriched