The Google ReCaptcha plugin supports 1.0 and 2.0 API calls.
Reuse of the getResponse() method is made use of for both API versions but 2.0 doesnt need/require the $challenge
This PR just silences strict warnings by setting the $challenge to `null and adds a tiny bit of additional documentation, cleans up a couple of other warnings and documents unused vars in method calls/signature
added spaces as requested