Mouse interface now almost done.

Mouse is set to stream mode and messages are shifted in. State machine
is now done. What is left to do is a good interface towards the memory
bus and some better data extraction. Mouse data cant be taken directly
from the mouse_data_packet shift register (since its a shift
register...). The data delivered to the memory bus should be the mouse
position, not velocity!

Led 0 and 1 show data and clock lines.
Led 2 to 5 show internal state.
Led 6 and 7 succesfully show left and right button presses!
Merge branch 'master' of https://github.com/ultralaserdeluxe/roej