Fixes #11 Adds changelog data to the API page and better API examples

- api.php gets changelog info added
- api/show.php has a few changes that allow us to show the json
  returned by the api call
- style.css gets modifications for those pages
Adds usage instructions for the setlistr_ruby library
Merge branch 'api_changes' of https://github.com/caprenter/Setlistr into api_changes
Adds support for setting site url to work against