Use Sinatra to serve pages

Sinatra will allow us to be more flexible going forward, using tools
like ERB templating and SASS stylesheets (http://sass-lang.com/)

This commit doesn't change the content of the site at all.
Update Gemfile to include Sinatra
Move index to views/index.erb
Extract common HTML into layout file
Extract sponsor sidebar into a partial
Move views from public/ to views, utilize layout
Serve print.css with SASS, add missing partial
Combine screen stylesheets to single SASS template
Add SASS dependency to Gemfile
Add missing fonts stylesheet
Merge pull request #4 from graysonwright/switch_to_sinatra

Use Sinatra to serve pages