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

Cleaned up BACnet/IP API a little.

bacnet-stack/ai.h

@@ -29,6 +29,10 @@
 #include <stdint.h>
 #include "bacdef.h"
 
+#ifdef __cplusplus
+extern "C" {
+#endif /* __cplusplus */
+
 bool Analog_Input_Valid_Instance(uint32_t object_instance);
 unsigned Analog_Input_Count(void);
 uint32_t Analog_Input_Index_To_Instance(unsigned index);
@@ -46,4 +50,8 @@ int Analog_Input_Encode_Property_APDU(
 void testAnalogInput(Test * pTest);
 #endif
 
+#ifdef __cplusplus
+}
+#endif /* __cplusplus */
+
 #endif