Make the GameOver exception inherit from SystemExit

Don't include embedded graphics in pew.py

pew.py contained embedded graphics for nice-looking pixels and
the game selection menu. This used up a lot of space. Now the
graphics for the pixels is generated on the fly, and the graphics
for the menu has been moved into the font.

Bump audio buffer to 128 bytes

Fix BGR/RGB colors for compatibility with DisplayIO

PewPew M4: improve reload on holding Z button

Reset PewPew M4 when Z button is held for 5s

Clean up pew.py

Optimize out GIF errors

Add support for PewPew M4

Make audiocore import work on older CircuitPython

If there is no audiocore, use audioio instead.