choose and execute an item within a list
demo_function_choice()
The function demo_function_choice choose and execute an item chosen in the variable 'demolist' that shall appear above. The variable 'demolist' is a text matrix whose first column contains item names displayed in an options window and whose second column contains the function that will be called. The title of the options window is 'Choose a demo'. If the options window is cancelled, the console is put back to its previous width.