[BRLTTY] Inka's non-standard flow control

[Jason White]

This thread originally began with a discussion of the non-standard serial
communication used by VisioBraille devices. The idea was to implement a
generic solution applicable to VisioBraille, INKA and, potentially, other
hardware having similar requirements.

I think that would be a reasonable plan, giving priority to supporting the
VisioBraille. Unlike INKA, from what I understood in the discussion, some
VisioBraille displays can't have their firmware updated so as to use standard
serial communication techniques.