Remove c2hs from the cabal build process for now

This is mostly motivated by issue #2: c2hs has trouble parsing
OpenBLAS's header files that involve the C99 _Complex type.  Since there
doesn't seem to be an easy way of fixing this other than fixing c2hs
upstream (even that is quite tricky: how would one marshal _Complex?),
c2hs will be removed from the cabal build process.

It's still part of the makefile build process (for developers), but
instead of using the system headers for Blas, it will use Netlib's
headers.  Some additional patching is done to make the generated Haskell
code more portable (see `src/BlasCTypes.hs`).