Introduce datatype for the Cabal index cache
Introduce datatype for the Cabal index cache

Right now this just wraps the list of cache entries, but this might make it
easier in the future to change the structure of the cache.

thomie/cabal,thomie/cabal,headprogrammingczar/cabal,gbaz/cabal,sopvop/cabal,headprogrammingczar/cabal,lukexi/cabal,kolmodin/cabal,randen/cabal,martinvlk/cabal,lukexi/cabal,garetxe/cabal,themoritz/cabal,sopvop/cabal,bennofs/cabal,Heather/cabal,Heather/cabal,themoritz/cabal,mydaum/cabal,gbaz/cabal,themoritz/cabal,garetxe/cabal,mydaum/cabal,bennofs/cabal,edsko/cabal,martinvlk/cabal,randen/cabal,kolmodin/cabal,edsko/cabal,sopvop/cabal