Update for AY1213/S2
Rearrange Lecture 1 .tex files
Added new "cf" environment for centralized large frame.
- modified upload script for DIY exercise
- update Makefile
- rename *-present.tex to *-show.tex
- tested with new cf environment
- new Problem Set 1
Added new folder for a slide library
- Lecture 3 added
- Fixed bug in cf environment (?)