add a cursor
add a cursor

required moving the write_board call into the block that only runs if a
button is pressed (otherwise it obliterates the blinker)

also just wrote the board once before looping, instead of forcing
animate the first time

also moved the animate clear to the top of the loop, which should mean
we get a new animate trigger, even if the last loop took longer than a
animation tick

beerriot/blockgame