Support for DEC special graphics

[Moult]

This is used in the majority of Nethack ttyrecs. There's a thing called https://en.wikipedia.org/wiki/DEC_Special_Graphics where if \e(0 is sent, it toggles some codes.

Steps to reproduce:

import pyte
screen = pyte.Screen(30, 1)
stream = pyte.Stream(screen)
data = b'x\x1b(0x\x1b(Bx'
stream.feed(data.decode('cp437'))
for y, row in screen.buffer.items():
    for x, cell in row.items():
        print(x, cell.data, cell.fg, cell.bg, cell.bold, "reversed" if cell.reverse else "")

import sys
sys.stdout.write(data.decode('cp437'))

Expected: x|x
Actual: xxx

Sample code produces:

0 x default default False 
1 x default default False 
2 x default default False 
x│x

[Moult]

As a workaround, I can set stream.use_utf = False.