void cmd_line(Shell &shell, int argc, const ShellArguments &argv){
  if(argc != 5){
    return;
  }

  long start[] = {atol(argv[1]), atol(argv[2])};
  long end[] = {atol(argv[3]), atol(argv[4])};
  artist.line(start, end);

  shell.write('x');
}
void cmd_origin(Shell &shell, int argc, const ShellArguments &argv){
  artist.origin();

  shell.write('x');
}