This separates the action of requesting an extent to be loaded from the action of requesting cached features. The renderer (or any other consumer of a vector source) calls load to request a data extent. A `featureload` event fires when new features are loaded. The renderer (or any other consumer) separately asks for cached features given an extent. This vector source only loads features once, but this separation will also work with sources that make multiple requests for data in different extents.
This also removes the `data` option from the vector source in favor of a `features` option. Since we no longer have shared data structures for geometries, people can manually create features and pass them to a vector source. The `addFeatures` method is exported as well. This is used to add features to a source that don't have a representation on the "remote" (or server).
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.
By maintaining separate R-Trees for each geometry type, we cover
the most critical query from the canvas renderer at higher
speeds. Using the filter's own evaluate method, we can now also
serve arbitrary queries, but they won't be fast.
Still needs unit tests.
Also trying to reference features directly here instead of
storing feature ids in the index. We'll see if this is good when
we have an index for tile coords as well and want to filter
with multiple filters, accessing multiple indices.
This needs more work still - see inline TODOs. It also has a
major bug - rendered vector features do not scale and do not
change their offset during panning. So only the initial view is
correct.
