Added Doxygen Modules describing the Object Helper Functions (and how they're used) and the Handler-to-Objects interface functions of the Device Object.

Two small code corrections in device.c:
a) Fixed the return value of Device_Write_Property() so that a -1 value would also return False.
b) Fixed the string length checked when writing PROP_OBJECT_NAME for the Device object.

bacnet-stack/include/readrange.h

@@ -125,6 +125,8 @@ typedef struct rrpropertyinfo {
     } RR_PROP_INFO;
 
 /** Function template for ReadRange information retrieval function.
+ * A function template; @see device.c for assignment to object types.
+ * @ingroup ObjHelpers 
  * @param pRequest [in]	Info on the request.
  * @param pInfo [out]   Where to write the response to.
  * @return True on success, False on error or failure.