This avoids features being rendered multiple times when they
cross tile borders. Currently this makes the style-rules.html
example extremely slow. Fix for that to come in my next commit.
The RTree can easily maintain an additional index dimension,
by passing a type with each added item. Now instead of
maintaining an RTree for each geometry type, we have a single
RTree with a type filter. With this change, using the RTree
finally speeds up rendering as expected.
Now vector layers can have a style. ol.Style instances have an
apply method to get the symbolizer literals for a feature. If the
layer does not have a style defined, there is also a static
applyDefaultStyle function on ol.Style to get the default
symbolizer literals for a feature. The vector layer also got a
groupFeaturesBySymbolizerLiteral method, which returns an array
with features grouped by symbolizer, as needed by the canvas
renderer.
