Add ol.Extent.getForView2DAndSize
Use ol.Extent.getForView2DAndSize
Optimize ol.Extent.getForView2DAndSize
Add ol.renderer.Layer.snapCenterToPixel
Use snapCenterToPixel in Canvas renderer
Use snapCenterToPixel in WebGL renderer
Use snapCenterToPixel in DOM renderer
Merge pull request #338 from twpayne/snap-center-to-pixel2

Snap center to pixel