Handle value printing where the result contains null characters

e.g.

   snprintf(buf, len, "'%c'", '\0')
Add a function for converting Bigarray.kind values to Ctypes.typ values.

See

   http://lists.ocaml.org/pipermail/ctypes/2013-December/000025.html

for background.
Merge pull request #114 from yallop/typ_of_bigarray_kind

Add a function for converting Bigarray.kind values to Ctypes.typ values.
Add raw_address_of_ptr, an inverse of ptr_of_raw_address.
Merge pull request #116 from yallop/raw_address_of_ptr

Add raw_address_of_ptr, an inverse of ptr_of_raw_address.