Add "hash encoding" to generate a value for unknown encodings.

For an unknown encoding, an arbitrary 32-bit value will be generated.

IRremote.h

@@ -56,6 +56,9 @@ private:
   long decodeSony(decode_results *results);
   long decodeRC5(decode_results *results);
   long decodeRC6(decode_results *results);
+  long decodeHash(decode_results *results);
+  int compare(unsigned int oldval, unsigned int newval);
+
 } 
 ;