Feature/timestamp messages (#68)

* added support for timestamps

* fixed tests

* Moved message class to own file; added 'z' to end of date strings

* added default time constructor

* removed unnecessary z

* added time string format info in comment

* changed from utc time to using local time

nuget.config

@@ -1,6 +1,7 @@
 <?xml version="1.0" encoding="utf-8"?>
 <configuration >
   <packageSources>
+    <add key="Nuget" value="https://www.nuget.org/api/v2" />
     <add key="DataTools Nuget" value="http://dtnuget/api/v2/" />
   </packageSources>
 </configuration>