Rephrase a bunch of things in the unlifted ffi types documentation. Add a section on pinned byte arrays.
Rephrase a bunch of things in the unlifted ffi types documentation. Add a section on pinned byte arrays.

sdiehl/ghc,sdiehl/ghc,sdiehl/ghc,sdiehl/ghc,sdiehl/ghc,sdiehl/ghc,sdiehl/ghc