Drop `mono'+, change `colour' and `uncolour' commands..

Drop `mono'+, change `colour' and `uncolour' commands..

Even after the new termcap/terminfo layer has been finished we
will have a chicken and egg problem regarding termcap
initialization and user colour setting commands, since the new
termcap interface has a *termcap-disable* setting which we really
want to adhere to, so we have to delay initialization until we
really enter interactive mode, long after reading rc files etc.

The only solution to allow the user to easily define different
modes for 256-colour mode and normal ANSI / ISO 6429 8-colour mode
is thus either to introduce a separate set of commands, or to
change the new current approach into a multiplexer series which
takes the desired "colour type", e.g., 256, 8, mono, iso etc., as
the first argument.

Go the latter way, thus drop `mono' / `unmono', and support a new
256 colour type for now.