Added svg versions of diagrams, centered diagrams, minor prettifying of latex.

I made some vectorised versions of the graphics in the whitepaper, and have put them in the public domain; they have been added to the whitepaper doc in the site. If there is an error loading the images, the page will fallback to the original png versions. I also centered the diagrams and slightly modified their widths. The LaTeX has been modified slightly to align the equality signs in the definition of variables.