Change stylesheet a little.
Remove extra json file
Exclude README file from final website
Rewrite project homepage

These edits try to give some more information on 'getting involved' and
add links to subprojects.
Finish restyling
Merge branch 'rewrite-homepage'

Several steps to improve the homepage
* Simplify the layout and design
* More emphasis on how people can help with the project
* Separate the material for the core textbook into a project-specific
  webpage.