Added characterstring change of value example (#175)

* Added characterstring change of value example

* Add COV to unit tests

* Add memcopy to object COV unit tests

Co-authored-by: Steve Karg <skarg@users.sourceforge.net>

test/bacnet/basic/object/av/CMakeLists.txt

@@ -42,9 +42,11 @@ add_executable(${PROJECT_NAME}
 	${SRC_DIR}/bacnet/bacstr.c
 	${SRC_DIR}/bacnet/bactext.c
 	${SRC_DIR}/bacnet/basic/sys/bigend.c
+	${SRC_DIR}/bacnet/cov.c
 	${SRC_DIR}/bacnet/datetime.c
 	${SRC_DIR}/bacnet/indtext.c
 	${SRC_DIR}/bacnet/lighting.c
+	${SRC_DIR}/bacnet/memcopy.c
 	./stubs.c
     # Test and test library files
 	./src/main.c