Remove unneeded function calls, rearrage for fused multiply–add, remove
excessive shader whitespace

ambientOcclusion -> ao per @WestLangley feedback here: https://github.com/mrdoob/three.js/pull/6263#issuecomment-83794671 #2

WebGLRenderer: Avoid flat shading buffer creation when using MeshPhongMaterial and clean up. See #6117.

use arguments variable to simplify ThreeJS error/warning handlers per @mrdoob's comments here: https://github.com/mrdoob/three.js/pull/5791#issuecomment-67733222

add THREE.error/THREE.warning to allow for easy redirection of THREE.js specific errors and warnings.

WebGLRenderer: Reverted non-hot-path Object.keys(). Moved hot-path ones to single-call paths. See #5186.

Added support for using a separate alpha map with MeshBasicMaterial, MeshLambertMaterial, and MeshPhongMaterial, and updated the OBJ converter to set materials as transparent if an alpha map is defined.

from the transforms that bind a THREE.Skeleton to a THREE.SkinnedMesh.  This
allows us to animate multiple THREE.SkinnedMesh instances with a single
THREE.Skeleton.

Here is a summary of the major changes:

extras/helpers/SkeletonHelper.js
* Fixed code mistakes (missing 'THREE').

objects/Bone.js
* Removed duplicate code that is already in THREE.Object3D.

objects/Skeleton.js
* Not a descendant of THREE.Object3D (previous version was).
* Stores boneMatrices and boneTexture.
* Independent of THREE.SkinnedMesh.

objects/SkinnedMesh.js
* Refactored boneMatrices and boneTexture related code into THREE.Skeleton.
* Added two bind matrix modes: "attached" and "detached".

renderers/WebGLRenderer.js
renderers/webgl/WebGLProgram.js
* Attach bindMatrix and bindMatrixInverse to shaders.

renderers/shaders/ShaderChunk.js
renderers/shaders/ShaderLib.js
* Use bind matrices during skinning.

If needed, source is retrievable by doing  renderer.context.getShaderSource( material.program.vertexShader );