Merge pull request #1462 from twpayne/vector-api-clean-ups

[vector-api] Minor clean-ups
Merge remote-tracking branch 'openlayers/master' into vector-api
Merge pull request #1464 from twpayne/vector-api-kml-linear-ring

[vector-api] KML LinearRing support
Use firstElementChild in ol.xml.parse
Use firstElementChild in ol.format.KML
Merge pull request #1466 from twpayne/vector-api-first-element-child

[vector-api] Use firstElementChild/nextElementSibling in XML parsers
Add comment about the rtree example not working when hosted
Merge pull request #1465 from twpayne/vector-api-rtree-example

[vector-api] Add comment about the rtree example not working when hosted
Fix rotation of WebGL tile layers
Merge pull request #1467 from twpayne/vector-api-webgl-rotation

[vector-api] Fix rotation of WebGL tile layers
Fix indentation in commments
Merge pull request #1468 from fredj/indent

Fix indentation in commments
Display attributions and logos for vector sources
Fix 'singleclick' in kml-timezones and kml-earthquakes examples
Add ol.render.IRender#drawAsync
Add ol.render.canvas.Immediate#drawAsync
Add ol.render.webgl.Immediate#drawAsync
Add ol.render.canvas.Replay#drawAsync
Use drawAsync in render box
Use drawAsync in canvas Immediate#drawFeature