Since there are no waypoints, do not attempt to optomize them.
google-map-directions no longer requires a map.

* google-map-directions can load the Maps API on it's own, a map is no longer used to tell when the API is ready.
* If a map is supplied, the results will be rendered on it.
* If a map is removed, the result rendering will be removed with it.
Add responseChanged to DRY up the directionsRenderer updating.
Small google-map-directions tweaks.

* Fire a google-map-response event when we have directions.
* Properly scope a bunch of stuff.
* Only try to render non-null responses.
Merge pull request #18 from bamnet/master

Allow google-map-directions to work without a map, close #15.