note new functions that xterm implements
note new functions that xterm implements

We never plan to implement any of the following, but xterm does, so it's
worth documentating what we are missing.

* DECSCUSR - Set cursor style
* DECSWBV - Set Warning-Bell Volume
* DECSMBV - Set Margin-Bell Volume

MarkLodato/vt100-parser,MarkLodato/vt100-parser