Processor-independent pin mapping feature.

- Cleaned up and organized pin mapping concept by @elmom.

- pin_map.h allows for user-supplied pin mapping and port vector
definitions in a centralized file. With more processor types, more
definitions could be added.

nuts_bolts.h

@@ -27,6 +27,7 @@
 #include <stdbool.h>
 #include "config.h"
 #include "defaults.h"
+#include "pin_map.h"
 
 #define false 0
 #define true 1