Add support for passing state through the KML parser.

Need a way to pass state about the URL for the KML into the
static methods of the parser.
Add helper method to get the full URL of relative images.

This provides support for KML files where the images may be relative
to the location of the KML file.  It attempts to determine if the
image url is absolute or relative.  If it is relative, then it
computes the full URL in relation to the KML file.
Handle case where some images return width 0.

Note sure why this happens, but need to handle this case so the images
will be displayed and scaled correctly.