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/rpm.h

@@ -52,6 +52,7 @@ typedef struct BACnet_Read_Access_Data {
 /** Fetches the lists of properties (array of BACNET_PROPERTY_ID's) for this
  *  object type, grouped by Required, Optional, and Proprietary.
  * A function template; @see device.c for assignment to object types.
+ * @ingroup ObjHelpers 
  *
  * @param pRequired [out] Pointer reference for the list of Required properties.
  * @param pOptional [out] Pointer reference for the list of Optional properties.