Help

- Made all the usage strings for the 'help' command consistent with the
  implementation and with visual alignment.

src/commands/CmdExport.cpp

@@ -38,7 +38,7 @@ extern Context context;
 CmdExport::CmdExport ()
 {
   _keyword     = "export";
-  _usage       = "task export [<filter>]";
+  _usage       = "task <filter> export";
   _description = STRING_CMD_EXPORT_USAGE;
   _read_only   = true;
   _displays_id = true;