Merge pull request #12 from fredj/plovr-download

Fix plovr download path
Fix bug where forEachVisibleLayer returned invisible layers
Add ol.Color
Use XYZ to indicate OpenStreetMap-style tile grids
Don't bother making forEachTileCoord abortable
Revert "add TileLayerRenderer.getPreferredZ_ plus tests". As noted by @twpayne, TileGrid.getZForResolution already returns the "preferred" z for an arbitrary resolution.

This reverts commit 8f5d0ac642686a9e156ad0cf480a33a8ec2b13c1.
refactoring, and renamings in tilegrid.js (related to continous zooming)
finish porting tschaub's infinite zooming work
Add ol.TileBounds.containsTileBounds
Add ol.TileBounds.equals
Add working WebGL renderer
Enable side-by-side DOM and WebGL demo
Add various FIXMEs
Rename redraw to render
Remove merged code
Clean up directory structure
Promote opacity/visibility changes into base class
Add hue and saturation controls, thanks @evanw
Sort properties
Add brightness and contrast controls, thanks @evanw