use .md extension
update synopsis wording
put a blank line after metadata
use tabs in HTML
use tabs in CSS
use HTML5
mv default.html base.html

I believe that `base.html` is a Django convention.  I think it better
reflects the root of hierarchical templates, while `default.html` is a bit
misleading since "default" is generally one of multiple options.
no title on root page
make width responsive

Note that this has not been tested on any browsers but Firefox.
update content layout and style