This moves the feature cache from ol.layer.Vector to ol.source.Vector. These are the minimum changes required to maintain the existing functionality and make tests pass. More refactoring to come.
This adds url, data and parser options to the source, and makes
EPSG:4326 the default projection. It also adds a prepareFeatures
method, which is used to load/parse data once the target
projection is known.
The first set geometry is considered the default. As an added bonus, we're back to a single argument constructor. Later, we could allow a schema to be set. This would be done before setting values (calling constructor with no args).