Move the help text for the 'O' command from the code into its own file
and allow that to be accessed from the '?' menu as well as by choosing
entry '?' in the 'O' menu.
sys/unix/Makefile.top has been updated to handle new 'optmenu', others
need to catch up. The game will still build and run without the file
but asking for options menu help won't work until they do.
