Cancel DCS with SUB, CAN, ESC or any CC1 code

Cancel DCS with SUB, CAN, ESC or any CC1 code

From http://www.vt100.net/docs/vt510-rm/chapter4:

	*The VT510 ignores all following characters until it receives a
	 SUB, ST, or any other C1 control character.

So OSC, PM and APC sequence ends with a SUB (it cancels the sequence
and show a question mark as error), ST or any another C1 (8 bits)
code, or their C0 (7 bits) equivalent sequences (at this moment we
do not handle C1 codes, but we should). But it is also said that:

	Cancel  CAN
	1/8     Immediately cancels an escape sequence, control sequence,
		or device control string in progress. In this case, the
		VT510 does not display any error character.

	Escape  ESC
	1/11    Introduces an escape sequence. ESC also cancels any escape
		sequence, control sequence, or device control string in
		progress.