Supporting inverted colors

More Select Graphics Rendition flags are evaluated, including
whether the text shall be inverted or not. <color> tags have
adjusted 'background' and 'foreground' attributes to show the
updated background/foreground color.
More color codes covered
Basic handling of Device Control Strings

Device Control Strings (DCS) are recognized and parsed,
but not interpreted in any way.
Removing ambiguous warning messages

Removing ambiguous and redundant warning messages about unknown escape
sequences. There is one 'else' clause at the end to catch all leftovers.