use pygeoifs feature collection instead of shapelys, add support for mixed shapely - pygeoif geometries for GeometryCollections

move geometries out of kml.Placemark int geometry.Geometry, add tests. The Tests for GeometryCollection fail if shapely is installed, waiting for guidance how to handle GeometryCollections with shapely

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