Various fixes + fix for chapter 5 in OPF.
* Greek is now typeset using math fonts.
* Removed parentheses from the numbered lists.
* Fixed chapter 5 path in OPF so it can be displayed again.
* Moved all non-font-size properties in CSS
  to font-size-relative units.
* Fixed math font size in headers.
Added fonts.
Added variable font size.
Updated README