Make sure we check for php://input in case a POST body is in there

It seem like the `$_POST` variable is just not set when performing POST operations that contain a JSON body. I apologize if any of this is silly, or I'm doing it wrong, but PHP is not my main language, and this seems to be a pretty common thing from what I can tell from StackOverflow ([example](http://stackoverflow.com/questions/1282909/php-post-array-empty-upon-form-submission)]

This seems like the right place to put this code as I think the `php://input` can only be called once. Please feel free to advise. 

I stumbled upon this when writing an integration for the new TestFlight webhooks beta.