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