Init
Release Lab 1
Nits in handin-prep script
Release Lab 2
Make grading script python2/3 compatible
Release Lab 3
Do handin-check before make handin
Release Lab 4
gradelib: Use bytes and bytearray types where appropriate

(patch 7c63faebf50a515f54d6a3fff63111f5034c77c0 from Austin)
Release Lab 5
lab 1 boot done
Merge branch 'lab1' into lab2
lab 2  vitrual memory
Merge branch 'lab2' into lab3
lab3 user environment  interrupt syscall
Merge branch 'lab3' into lab4
lab4 Preemptive Multitasking done
Merge branch 'lab4' into lab5

Conflicts:
	kern/env.c
	kern/init.c
lab 5 filesystem