cPeristence.h:
    remove unused #define
    remove decl of cPersistenceCAPI from header and put in cPersistence.c

cPersistence.c:
    remove several unused functions and decls
    update K&R style func decls
    make func decls prototypes when needed
    add module doc string

    Remove PyErr_Occurred() check from the end of the module,
    following current best practice for Python.