Until we know what we want to return, return undefined
Interface for GetFeatureInfo

When a source implements this interface, the layer renderer can
access the source to get feature info.
Implementing GetFeatureInfo for WMS
Add example, and use getFeatures in other examples

The new dedicated getfeatureinfo example shows how to combine
feature info from a WMS and a vector layer. The other examples
that previously used getFeatureInfo from vector layers now use
the more appropriate getFeatures.
Adding tests, and fixing an issue revealed by the tests
Move attributions constant to constructor
Merge pull request #890 from tschaub/attributions

Move attribution constants to constructors.
Support fillOpacity and strokeOpacity on shape symbolizers
Rename line symbolizer opacity to strokeOpacity for consistency

We already have strokeColor and strokeWidth.  Having strokeOpacity makes sense.
Support fillOpacity and strokeOpacity on polygon symbolizers
Optionally stroke and fill polygons (closes #475)

This also removes the unsupported width property from PolyStyle (closes #891).
Separate opacity in examples
Use plovr-81ed862
Merge pull request #893 from twpayne/plovr-81ed862

Use plovr-81ed862
Merge pull request #892 from tschaub/symbolizer-opacity

Separate fill and stroke opacity.
Provide a method for parsing any GeoJSON as an array of features
No array needed for a single event

Thanks @bartvde.
Merge pull request #894 from tschaub/more-geojson

Allowing all GeoJSON types to be read as an array of features.  This makes the parser more useful when used with a source that may not already be a feature collection.
Use X, Y or I, J depending on WMS version

This also adds consistency - Pixel coordinates are now always
rounded to integers.
Fixing example title

Thanks @bartvde for catching this.