Give me my $_POST, or a JSON helper for CodeIgniter

In a current Project I’ve been working with a Cappucino frontend and a CodeIgniter Backend. Since Cappucino just loves JSON I decided this is the way to go, sadly PHP doesn’t provide a standard way to interact with a JSON POST but with a little helper this can be solved easily. I made a Gist out of it so it can be improved apon and reused.