pstat5a: added lecture 5
m108b: added discussion for class week 2
m103: added lec. 4 & 5 PDFs and lec. 4 notes; 108b: added lec. 5 & 6 powerpoints and first discussion section notes; 103 lab: edited cheek cell (photoshop for better histogram); pstat5a: lecture 4 PDF and lecture 6 notes