This is now a fully vt500-series compliant state machine that parses escape
sequences. See vt100.net/emu for information on this state-machine. This is
written from scratch, though.
It now handles all kind of escape sequences that we every want to support. It
correctly ignores all unsupported ones right now.
Signed-off-by: David Herrmann <dh.herrmann@googlemail.com>