fixed vm/mmap-close
Merge remote-tracking branch 'origin/ben_dev' into ralph_swap

Conflicts:
	src/userprog/syscall.c
Merge remote-tracking branch 'origin/ben_dev' into ralph_swap
Merge remote-tracking branch 'origin/ben_dev' into ralph_swap
Corrected synchronization for swapping. Need to implement page-parallel
Corrected synchronization for swapping. Need to implement page-parallel
still need to fix synchronization errors
Wrote design doc and cleaned up page.c