Ctypes_bigarray.address ~> unsafe_address, and remove an unused parameter.
Change ctypes_(read|write)_pointer to operate on fat pointers.
Convert ctypes_memcpy_fat to take a fat_ptr for the destination address.
Convert ctypes_read to take a fat pointer.
Convert ctypes_write to take a fat pointer.
Implement to_voidp and from_voidp in terms of castp; remove an unused cast.