-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
It should be able to parse escape sequences up to VT300, but not everything
is implemented. Most notably, there is no font handling - all displayable
characters are handed to the graphics driver. To solve this, a serious
interface change to the graphics driver is needed (Unicode?).
