do not import geometries in __init__.py as they are imported from PyGeoIf or Shapely which may not be available (e.g for buildout)

move from lists to generators to fetch the contents of a container or kml, use getter and setter for feature.styleUrl

add geometry.py for geometry definitions, add base.py for a common base classes used in kml and styles, add timespan and timestamp elements to kml.py

make sure that the output (to_string) can be fed back into from_string and produces the same document