Added resource/include/OCRepresentation.h to Doxyfile

Added resource/include/OCRepresentation.h to Doxyfile

OCRepresentation is passed as a paramter to documented API calls, so
presumably, it should be part of the public, documented API.

Change-Id: Ia17813b8ade749d0446d1ed4068f7e49d60d6ec4
Signed-off-by: William Dieter <william.r.dieter@intel.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/351
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: Erich Keane <erich.keane@intel.com>
Reviewed-by: Sudarshan Prasad <sudarshan.prasad@intel.com>