Merged most of Etienne's improvements from last year, including
treee64f87b4ccf5bcb2aa516fab12fdf9de3f36cc1b
-rw-r--r-- 10475 library.scm
-rw-r--r-- 65437 picobit-vm.c
-rw-r--r-- 112403 picobit.scm
-rw-r--r-- 388 red-green.scm
-rw-r--r-- 31589 robot.scm