represent it as U+2500 (BOX DRAWINGS LIGHT HORIZONTAL). This makes NetHack
DECgraphics mode work properly on a wscons console using an IBM-encoded font.
-display DEC special graphics and DEC technical characters as far as
possible
-implement the font switching controls (need documentation!)
-behave well if double-width characters are requested
-simplify the state machine: store CSI command modifiers in variables
instead of dedicating own states to each of them