Added the capacity to decode JSON from php://input

If you transmit data using Content-Type: application/json, we need to decode the JSON data to an array, fallback's to string if it's not a valid JSON string.

Also, I've changed $_REQUEST for $request_params since we already affect that variable with the request method data and the csurl variable may come from this JSON string. 

I needed this when making POST request with AngularJS, as its default object serialization is JSON.