Adding iterator reset for Rules iteration (#59)

When iterating over a Rules object, the iteration would work for a
single pass before throwing a StopIteration exception. This slightly
changes the iteration logic to reset to the iteration list head after
a full iteration has been completed.

yara-python.c

@@ -1278,6 +1278,7 @@ static PyObject* Rules_next(
 
   if (RULE_IS_NULL(rules->iter_current_rule))
   {
+    rules->iter_current_rule = rules->rules->rules_list_head;
     PyErr_SetNone(PyExc_StopIteration);
     return NULL;
   }