Fix zip_import.c's read_directory() to use appropriate types for the values

Fix zip_import.c's read_directory() to use appropriate types for the values
being read from the header vs the values being used by fseek and ftell
(Py_ssize_t for those) and how they are computed.  Py_ssize_t is used for
actual file offsets so that files greater than 2gigs could be supported.
Updates the Py_BuildValue format string to match (including several existing
wrong 'i's that should have been 'l's).