Adding the ability to give flexible headers and content type

Example in the JS code is:
        bgGeo.configure(callbackFn, failureFn, {
                        url: ‘somewhere + UUID, // <-- only required
for Android; ios allows javascript callbacks for your http
                        params: {
        // HTTP POST params sent to your server when persisting
locations.
                        },
                        headers: {
                                "Content-type":
"application/x-www-form-urlencoded",
                                "auth_uuid": UUID,
                                "auth_token": TOKEN,
                        },
                        desiredAccuracy: 10,
                        stationaryRadius: 20,
                        distanceFilter: 30,
                        debug: true // <-- enable this hear sounds for
background-geolocation life-cycle.
                        });
missing paren
Adding Iterator for headers
finish headers
Fixing spacing issue
Fixing another space issue
Fixing another other space issue
Fix merge conflicts due to previous PR appending params
Merge branch 'zgiles-flexibleheaders'