Updates to Externs File for Maps V2 API

Kai found some missing items in my Maps V2 externs file. I was missing methods from the following classes: GControl, GMapType, GMarker, GProjection, and GTileLayer. I also apparently missed GPolyline.fromEncoded() and GPolygon.fromEncoded() because they were listed under Factory Methods, which my script did not know to look for.

Apparently Kai has also found an inconsistency between the online documentation for GPolyline.fromEncoded() and its implementation, but I want to get someone from the Maps team to confirm before updating that.