First take at converting lab 6 -- needs lots of edits, including explaining the algorithm, since there is no textbook to explain it
Updated the daily announcements for tomorrow
Updated the AVL worksheet to have the name on the reverse side as well
Updates from today's lectures, including some more AVL trees
Skeleton change: read from stdin as per lab doc.

NB POSSIBLE AUTOGRADER BREAK

Lab doc told students to use
    ./a.out < testfile.txt
to run their code; however the program actually took in a filename on
stdin.

Modified the code to read its input from stdin. Other option was to
update the lab document, but this is easier & more amenable to
autograding- that said, the autograder is probably not yet set up to use
this input format.