Revised FFI syntax + typing

[Sven Panne]

Simon Marlow wrote:
> A totally minor point, but 'wincall' doesn't feel right. [...]
> I'd stick with 'stdcall' because that's what everyone else seems to call
> it.  gcc has a 'stdcall' function attribute, BTW.

OK, so let's forget about 'wincall' and continue using 'stdcall'.
Inventing new names for things already in existence is not a very
good plan.

> Why is Word a GHC extension?  Someone remind me?

Hmmm, I thought that the Word type itself is a GHC extension, the
hslibs docs for module Word only talk about the explictly sized
variants. OTOH the implementation exports Word, but for legacy
reasons, IIRC. If this is really the case, we should document this
somehow in the sources.

Cheers,
   S.