Deriving Typeable to work with ghc 7.8.

Signed-off-by: Philipp Kant <philipp@infinipool.com>
Got HList.hs to compile with ghc 7.8.2

I had to drop the functional dependency in HList2List, since it cannot
be satisfied for the empty list.

Disentangled kind and type variable names in type family ($).

Signed-off-by: Philipp Kant <philipp@infinipool.com>