no DBCS in WIDTH 40 and 20 modes
fixed DBCS blink palette glitch
added backend_cli --cli for better command-line interface. --dumb is now --filter.
simplified dumb terminal to filter-only, should also work on Windows
backend_dumb renamed novideo
replace hard-coded esc sequences with constant
novideo backend always initialises
novideo backend no longer uses the echo system
fix for LOCATEd text in command line interface