More realistic bench

[fabi321]

The current bench only uses the PX x y rrggbb command, but irl usage would probably use a combination of rrggbb, rrggbbaa, gg as well as OFFSET commands. One possible way to accomplish this would be by using an actual client lib, as building a command using all commands together would probably be tedious at best. Usage of HELP and SIZE is probably low that I think they can be omitted from the bench.