Feature/bacnet discover dnet devices (#583)

* Added an example application to discover devices and their objects and properties on a specific destination network. The application uses a BACnet Discovery FSM module along with the BACnet R/W FSM.  The BACnet Discovery module stores the binary property data in Keylists and includes device object property queries and iterators.

* Added callback from BACnet R/W FSM module for I-Am messages.

* Removed dependency in BACnet R/W FSM module on rpm_ack_decode_service_request() which uses calloc/free value lists.  Created an alternate RPM-ACK to RP-ACK processing function.

* Changed RPM handler to skip over unknown property values

src/bacnet/property.c

@@ -1535,7 +1535,7 @@ BACNET_PROPERTY_ID property_list_special_property(
     BACNET_PROPERTY_ID special_property,
     unsigned index)
 {
-    int property = -1; /* return value */
+    BACNET_PROPERTY_ID property = UINT32_MAX; /* return value */
     unsigned required, optional, proprietary;
     struct special_property_list_t PropertyList = { 0 };
 
@@ -1573,7 +1573,7 @@ BACNET_PROPERTY_ID property_list_special_property(
         }
     }
 
-    return (BACNET_PROPERTY_ID)property;
+    return property;
 }
 
 unsigned property_list_special_count(