Modify interaction doesn't need to store styles
Use minus sign as zoom out label
Better code formatting
Merge pull request #1711 from elemoine/modify

Modify interaction doesn't need to store styles
Merge pull request #1713 from elemoine/zoomcontrol

Use minus sign as zoom out label
Add opacity property to ol.style.Image
Handle image opacity in ol.render.canvas.ImageReplay
Handle image opacity in ol.render.canvas.Immediate
Set ol.style.Icon opacity
Dispatch 'render' event in renderer.canvas.VectorLayer

The context property of the event only contains the vector rendering.
Add ol.layer.Heatmap class and example