add command-Q to quit.
Since ROM 1 doesn't have _RemoveCDA in ROM, the control panel is only installed in ROM 3.
(TODO -- check at runtime in case launched from GS/OS)
This is fixed in ROM 3 (or via the TS patches if you boot GS/OS).
Workaround it by switching to DPAGE 0.
Also, allocate memory (since I originally thought that might be relevant).
based on testing, this applies to vt52 and vt100.
use the current x pos to choose between $56 and $57 (mouse text checkerboard)
so multiple characters look pretty.
this also adds a hexdump in the CDA for the outgoing buffer
in local mode, "incoming" data is read from the outgoing buffer.
Currently data is (potentially) sent on each run of the main loop.
I thought about using the TX empty interrupt but it still needs to be
kicked off at some point (unlike incoming data)
to handle DECAWM mode, bit 7 of x ($80 + 79) indicates a wrap is imminent, as opposed to just being in column 79. backspace, etc will drop back to column 78 (based on testing).
