Created doc/doc/extra_files directory for files that should show up in root of clawpack.github.io, and modified conf.py to add this directory in html_extra_path
change CNAME to clawpack.org and document new way to push webpages
fixed pointer to github.io/doc
fixed _templates/index.html
Merge pull request #66 from rjleveque/extra_files

Created doc/doc/extra_files directory