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

Cleaned up BACnet/IP API a little.

bacnet-stack/wp.h

@@ -75,6 +75,10 @@ typedef struct BACnet_Write_Property_Data
   uint8_t priority; // use 0 if not setting the priority
 } BACNET_WRITE_PROPERTY_DATA;
 
+#ifdef __cplusplus
+extern "C" {
+#endif /* __cplusplus */
+
 // encode service
 int wp_encode_apdu(
   uint8_t *apdu, 
@@ -100,5 +104,9 @@ void test_ReadProperty(Test * pTest);
 void test_ReadPropertyAck(Test * pTest);
 #endif
 
+#ifdef __cplusplus
+}
+#endif /* __cplusplus */
+
 #endif