Conditionally render JSONP

[joeyespo]

Here's my attempt to fix #3.

Pros

• This allows you to use a JSON endpoint normally
• This complies with the expected JSONP behavior that wraps your JSON when a callback parameter is provided (and defaults to 'callback' when no value is specified) or application/javascript is used
• No custom code needed in your view function

Cons

• The media_type is now set to application/json from JSONRenderer (and therefore, if callback is provided without explicitly requesting the proper application/javascript content type, it will respond with application/json)

There's another solution from the docs that demonstrates how to use multiple renderers (based on accepted media type). That method would allow you to use application/javascript again to eliminate the above con, but if you're manually doing that, you may as well manually wrap your json too without this plugin. Because you want to cut down on verbosity, the pros may outweigh the con.

Also, Chrome didn't complain when I tried <script src="myendpoint?callback=mycallback">. And jQuery uses the right media type when using JSONP, so no issue there.

Thoughts?