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/Context.cpp

@@ -221,6 +221,7 @@ int Context::dispatch (std::string &out)
   else if (cmd.command == "_commands")     { rc = handleCompletionCommands (out); }
   else if (cmd.command == "_ids")          { rc = handleCompletionIDs      (out); }
   else if (cmd.command == "_config")       { rc = handleCompletionConfig   (out); }
+  else if (cmd.command == "_version")      { rc = handleCompletionVersion  (out); }
   else if (cmd.command == "" &&
            sequence.size ())               { rc = handleModify             (out); }