Change the inner workings of the experimental TTY_PERM_INVENT.
Switch to delivering the content to tty for the experimental perm_invent
via the existing window port interface (start_menu(), add_menu(), end_menu).
This also adds a new window port interface call ctrl_nhwindow() for
delivering information to the window port, and/or obtaining specific
information from the window port. The information and requests can
be extended as required. To be documented later once the changes settle
down.
Due to the intrusive nature of these changes and the possibility of
some bugs in the new code, I'm going to leave TTY_PERM_INVENT commented
out in the repository for a day or two. Anyone wishing to test it out
can do so by uncommenting TTY_PERM_INVENT in config.h.
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