Dropped Convert::toJSON()

In an effort to only maintain compatibility with the latest version of PHP (currently the 5.5 branch) I dropped the sanity checks if `json_encode` was available as it is always available in PHP 5.2+. Dropping this sanity check also allowed me to remove the wrapper function and the `JSON_AVAILABLE` constant. Ideally I'd like to move towards dropping the `Convert` class entirely but will need a way to convert an array to XML as the `RSS` class still leverages it. One thought is to move that code right into the `RSS` class as it never gets used elsewhere because XML is gross.
Stated intentions for being bleeding edge.
Hacked in pretty JSON option

Just need to include `?pretty=true` to a request and the JSON returned will be formatted. As I was digging in there I think I may consolidate all of the Display logic into a single class and potentially bring back `.json` and `.xml` extensions to dictate what is returned. Would help a ton in scenarios where I have an endpoint that I want to server up a template on error or return JSON on success.
Merge branch 'master' of github.com:joshtronic/pickles