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.

doc/htdocs/index.html

@@ -958,6 +958,13 @@
         <td bgcolor="#FFFFDD" width="25%" align="center" valign=
         "top">Yes</td>
       </tr>
+      <tr>
+        <td bgcolor="#FFFFDD" width="75%" valign="top"><a href=
+        "https://sourceforge.net/p/bacnet/src/ci/master/tree/src/bacnet/basic/object/timer.c">
+        Timer</a></td>
+        <td bgcolor="#FFFFDD" width="25%" align="center" valign=
+        "top">Yes</td>
+      </tr>
       <tr>
         <td bgcolor="#FFFFDD" width="75%" valign="top"><a href=
         "https://sourceforge.net/p/bacnet/src/ci/master/tree/src/bacnet/basic/object/iv.c">