Feature - simple version report for scripts

- Added a simple _version command that displays only the version
  number and a newline.  This makes it easier for external task support
  scripts to determine which version of task is installed - easier than
  parsing the version command output.

src/command.cpp

@@ -373,6 +373,16 @@ int handleCompletionConfig (std::string &outs)
   return 0;
 }
 
+////////////////////////////////////////////////////////////////////////////////
+// A simple version display for use by completion scripts and the task-update
+// script.
+int handleCompletionVersion (std::string &outs)
+{
+  outs = VERSION;
+  outs += "\n";
+  return 0;
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 int handleCompletionIDs (std::string &outs)
 {