Added externs declarations to header files to handle C++ compilation.

Cleaned up BACnet/IP API a little.

bacnet-stack/rp.h

@@ -47,6 +47,10 @@ typedef struct BACnet_Read_Property_Data
   int application_data_len;
 } BACNET_READ_PROPERTY_DATA;
 
+#ifdef __cplusplus
+extern "C" {
+#endif /* __cplusplus */
+
 // encode service
 int rp_encode_apdu(
   uint8_t *apdu, 
@@ -89,5 +93,9 @@ void test_ReadProperty(Test * pTest);
 void test_ReadPropertyAck(Test * pTest);
 #endif
 
+#ifdef __cplusplus
+}
+#endif /* __cplusplus */
+
 #endif