Added support for KML StyleMap element

Added support for the KML element StyleMap, see:
https://developers.google.com/kml/documentation/kmlreference#stylemap

Only the 'normal' key-pair is added to the array of existing styles not the 'highlight' one.

New function "parseStyleMap" was added, and is called just after the existing parsing of the KML Style element.
Merge pull request #87 from opie/master

Added support for KML StyleMap element