Fixing a type mistake (size parameter type inside engine.createRenderTargetTexture is "any").
Adding a ReadPixels method, to wrap WebGL call.
Adding a CreateScreenshot method inside BABYLON.Tools, to make a render of the scene, and automatically download it as a .png
Merge remote-tracking branch 'remotes/BabylonJS/master' into ScreenShotFeatureTS

Conflicts:
	Babylon/Tools/babylon.tools.js
	Babylon/Tools/babylon.tools.ts
	Babylon/babylon.engine.js
	Babylon/babylon.engine.ts
Adding some comments to explain how things work.
Rename size.zoom to size.precision (more explicit).
Merge pull request #188 from nicolas-obre/ScreenshotFeature

Screenshot feature