Improvements from Oxy patch

Original email reads...
It does not contain any fundamental changes or new functions but a lot of improvements which I have done over time (added several const/static specifiers, replaced repeated if-conditions by if-else, removed some warnings).

backend/auspost.c

@@ -109,7 +109,7 @@ int australia_post(struct zint_symbol *symbol, unsigned char source[], int lengt
     unsigned int loopey, reader, h;
 
     char data_pattern[200];
-    char fcc[3] = {0, 0}, dpid[10];
+    char fcc[3] = {0, 0, 0}, dpid[10];
     char localstr[30];
 
     error_number = 0;