Make <Typeable.h> obsolete and refactor away its use
With GHC 7.8's PolyKinds the macros in <Typeable.h> are no longer of any
use, and their use is clearly obsolete. The sites using those macros are
replaced by auto-derivations of Typeable instances.
This reduces reliance on the CPP extension and the compile dependency on
Typeable.h in a couple of modules.
Signed-off-by: Herbert Valerio Riedel <email@example.com>