Let's have an abstract 'printer' class.
Hoist the integer printer too
Save a few bytes in the Display class
Let's have microsecond delays too
Simplify the Print subclass (at the cost of performance)
Let's have a really, really simple printf
How about a transmit-only bitbang serial port?
Use the serial port for debug output
fix elapsed time calculation
Add %x format to printf
add %p format and use it for panic callers
move debug output to the main loop and serial