Prints out a rightclick menu on right-click.
The character string is menu item text, and the function is picked from the list defined below.
SYSTEM MENU FUNCTION CONSTANTS:
skip…same as 「skip to next choice」
reset…reset program
save…go to save menu
load…go to load menu
lookback…go to log mode
windowerase…minimize window
EX）
rmenu "SAVE",save,"LOAD",load,"LOG",lookback