* convert to ES modules

* rebuild

* move shaders back into glsl files

* reinstate polyfills

More precision is used for the green channel in RGB565 and DXT texture formats, so this would improve the quality in those cases.

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.

Fixed shader whitespace to comply with new style

Conflicts:
	src/renderers/shaders/ShaderChunk.js
	src/renderers/shaders/ShaderLib.js

All the skinning examples seem to be working fine still.

- split up files
- added new files descriptions to docs

This commit fixes a skinning bug that occurs when two or more SkinnedMesh objects share a common material and have bone textures of different sizes.  Currently, bone texture sizes are hard coded into the shader program, requiring the program to be re-built when the bone texture size changes; however, the current implementation does not handle this correctly, which can lead to the shader accessing incorrect bone transforms.

This commit uses two uniforms to store the bone texture dimensions.  These uniforms are updated as needed, eliminating the need to re-build the shader and fixing the bug.

Renamed ShaderLib's 'normal2' shader to 'normalmap' as suggested in 4276c9f5.

ShaderUtils relied on ShaderChunks so this created troubles when trying to use three-canvas and three-extras. Besides, better to keep a single library of shaders.

Taking into account also original material texture (if it exists).

Added shadow map type definitions and replaced shadowMapSoft boolean on the renderer with shadowMapType. The default type is THREE.PCFShadowMap, which amounts to the previous default of shadowMapSoft = true. A new type, THREE.PCFSoftShadowMap will enable bilinear filtering of the shadow in the shader for smoother results.

Moved bilinear filtering of shadow maps into the shader. Previously, the filtering on the shadowmap was set to linear outside of the shader and this doesn't work for filtering a depth comparison. For PCF, the filtering needs to be done post-depth-comparison. i.e. in the shader.