Added basic timer object, internal state machine, and unit tests (#1123)

* Added basic timer object, internal state machine, and unit tests

* Added BACnetTimerStateChangeValue encode, decode, parse, print, and diff with unit tests

* Changed handler of add/remove list element to check if the property is a BACnetLIST

* Added BACnetLIST utility for handling WriteProperty to a list.

* Fixed outlier ReadProperty object handlers to return zero when the RP parameter is NULL.

ports/at91sam7s/CMakeLists.txt

@@ -168,6 +168,7 @@ set(BACNET_PROJECT_SOURCE
     ${LIBRARY_BACNET_CORE}/reject.c
     ${LIBRARY_BACNET_CORE}/rp.c
     ${LIBRARY_BACNET_CORE}/rpm.c
+    ${LIBRARY_BACNET_CORE}/timer_value.c
     ${LIBRARY_BACNET_CORE}/timestamp.c
     ${LIBRARY_BACNET_CORE}/weeklyschedule.c
     ${LIBRARY_BACNET_CORE}/dailyschedule.c

ports/at91sam7s/Makefile

@@ -130,6 +130,7 @@ CORESRC = $(BACNET_CORE)/abort.c \
 	$(BACNET_CORE)/reject.c \
 	$(BACNET_CORE)/rp.c \
 	$(BACNET_CORE)/rpm.c \
+	$(BACNET_CORE)/timer_value.c \
 	$(BACNET_CORE)/timestamp.c \
 	$(BACNET_CORE)/weeklyschedule.c \
 	$(BACNET_CORE)/dailyschedule.c \

ports/at91sam7s/bacnet.ewp

@@ -1188,6 +1188,9 @@
         <file>
             <name>$PROJ_DIR$\..\..\src\bacnet\rpm.c</name>
         </file>
+        <file>
+            <name>$PROJ_DIR$\..\..\src\bacnet\timer_value.c</name>
+        </file>
         <file>
             <name>$PROJ_DIR$\..\..\src\bacnet\timestamp.c</name>
         </file>