initial commit

Basic cragslist mockup
changed db to postgres for heroku
config.asset compilition in config/environments/production.rb
made some changes to whitespace handling and sanitized form data
fixed links in category views

Links should link to the listing within the category
(not the listings/:id link), to mimic craigslist's
routing conventions
fixed links
DRY up views and fix id bug

posting ID was not getting rendered from model,
causing craigsdiff example to not work correctly
added jquery gem
javascript configuration

- Craigsdiff javascript was loading unnecessarily on static_pages
  causing js errors to be thrown. Changed asset compilation
  configuration so they it only be sent on listing pages.
Added modals to explain how to use the craigsdiff demo