Fixed a bug (width and height were swapped)

Aaand now it's actually correct. Sorry.

Corrected a long standing bug in the gradient computations. Not a fatal bug, but it improves the accuracy slightly.

Made the license match my promise (chaged from GPL to MIT)

added missing test images

Added missing GLSL version of the anti-aliased Euclidean distance transform

Removed restrict to workaround driver bug

Removed restrict to workaround driver bug.

Fixed SpiderGL link

Added Shalini's chapters

Added url to README.md

Added chapter 20

Added all the other chapters

Added chapter 15

Added chapter 11