This changes startup so we get the size of the current terminal
to send to Urbit on startup. We then subscribe to terminal size
change notifications and send those to your Urbit via the terminal
muxing system.
In the case where there are multiple terminal connections to your
Urbit, set the terminal size to the minimum of the widths.
If you connect to an urbit using the remote terminal code,
slogs would not be printed to them since they were hard
coded to be printed to stderr. This threads slog printing
to the terminal driver, and puts them in scrollback.
(It does not actually fix slogs being printed on one line.)
