The `WebGLRenderer.rebindPipeline` method has been changed slightly. Previously, you had to specify the `pipelineInstance`, but this is now optional. If you don't, it will use the new `previousPipeline` property instead. If not set, or none given, it will now return without throwing gl errors as well.
* `WebGLRenderer.normalTexture` is a new property that holds the currently bound normal map (texture unit one).
* `WebGLRenderer.setNormalMap` is a new method that sets the current normal map texture.
* `WebGLRenderer.clearNormalMap` is a new method that clears the current normal map texture.
* `WebGLRenderer.resetTextures` is a new method that flushes the pipeline, resets all textures back to the temporary ones and resets the active texture counter.
* `WebGLRenderer.setTextureZero` is a new method that activates texture zero and binds the given texture to it. Useful for fbo backed game objects.
* `WebGLRenderer.clearTextureZero` is a new method that clears the texture tha was bound to unit zero.
* `WebGLRenderer.textureZero` is a new property that holds the currently bound unit zero texture.
* The property `WebGLRenderer.currentActiveTextureUnit` has been renamed to `currentActiveTexture`.
* `WebGLRenderer.startActiveTexture` is a new read-only property contains the current starting active texture unit.
* `WebGLRenderer.maxTextures` is a new read-only property that contains the maximum number of texture units WebGL can use.
* `WebGLRenderer.textureIndexes` is a new read-only array that contains all of the available WebGL texture units.
* `WebGLRenderer.tempTextures` is a new read-only array that contains temporary WebGL textures.
* The `WebGLRenderer.currentTextures` property has been removed, as it's no longer used.
* `WebGLRenderer.currentTextures` has been removed, as it's no longer used internally.
* `WebGLRenderer.setBlankTexture` no longer has a `force` parameter, as it's set by default.
* `WebGLRenderer.setTextureSource` is a new method, used by pipelines and Game Objects, that will assign a texture unit to the given Texture Source.
* The `WebGLRenderer.setTexture2D` method has been updated to use the new texture unit assignment. It no longer takes the `textureUnit` or `flush` parameters and these have been removed from its method signature.
