set up print chains for 'Guess:', 'Up' and 'Down'
now prints Up and Down depending on what number was entered
now responds Up to 0
corrected comment
now works almost as intended

only missing some up/down messages on the second guess
now correctly switches direction for corner cases; still prints nothing for cases 3->4 and 5->4
now handles 3->4 and 4->3 etc correctly
corrected comment
Merge branch '01-higher-lower'