Update previous lectures

- move some stuff around
- change the name of the first lecture
fix link to introduction
overview of lecture 4
Fix errors in tutorial

Thanks to lisa for spotting those bugs!
New folder with exercises
add new exercises
Add links to demos and exercises
Basic layout for demos
Add demos

- 10 PRINT processing sketch
- 10 PRINT Webfont example page
- Elemenrary CA Mathematica Package
- Elementary CA Mathematica Notebook
Merge remote-tracking branch 'Martin/master'
Minor change.