Add option priorities

For instance, filename= must come after directory= or things will
go wrong. So add a priority value to each option, so that the parser
will take that into account.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/fio.h b/fio.h
index 207b2ec..ff4668e 100644
--- a/fio.h
+++ b/fio.h
@@ -820,7 +820,7 @@
  * Init/option functions
  */
 extern int __must_check parse_options(int, char **);
-extern int fio_option_parse(struct thread_data *, const char *);
+extern int fio_options_parse(struct thread_data *, char **, int);
 extern int fio_cmd_option_parse(struct thread_data *, const char *, char *);
 extern void fio_fill_default_options(struct thread_data *);
 extern int fio_show_option_help(const char *);