Plugin jsonp

Plugin to highlight JSONP responses, with in-built functionality to extract file data from Github and Bitbucket requests. Inspired from #240.

While this _could_ be achieved by modifying File Highlighter (e.g. #208), not all hosts are going to have CORS enabled, and one may genuinely want to highlight JSONP responses (perhaps some server status, per the examples page).

Live demo of this branch at http://nauzilus-prism.azurewebsites.net/plugins/jsonp-highlight/
You could then add some documentation here in the way of 
"return a string, if your handler understands and supports the given response, `null` if it doesn't support it"