Pushed REVISION to 29.

GouraudShading and PhongShading ⟶ SmoothShading

Render first objects / material groups that use normal blending, then render ones which use additive blending.

Proper solution should be: sort triangles by blending, render all the normal ones, sort additive ones by depth and then render them back to front.

http://www.opengl.org/resources/faq/technical/transparency.htm
http://nehe.gamedev.net/data/lessons/lesson.asp?lesson=08

While this is acceptable in C++ / OpenGL, with JavaScript / WebGL this would kill the performance (you would need to sort triangles in JS and also create new buffers every frame).

Also tried to come up with subtractive / darken blending, but didn't find any satisfactory formula :(.

* Changed THREE.Vertex.positionScreen from a Vector3 to a Vector4 to support clipping.

This is actually tricky due to multimaterials and vertex normals.

The practical effects of "shading" parameter in WebGLRenderer are currently following:

- if your model has vertex normals, now you can "dumb down" its shading by specifying THREE.FlatShading for MeshLambertMaterial and MeshPhongMaterial
- if your model has only face normals, it will always have just flat shading, no matter which shading you set, no escape from this
- if your model has multiple materials, smooth shading always "wins", meaning if there is at least one smooth shaded material in multimaterial group, all other materials in this group will be also smooth shaded (this is solvable by having multiple normal buffers, but seems wasteful, at least for the moment, till there are no practical use cases)

Currently implemented shading / material combinations:

  - MeshNormalMaterial: FlatShading [default], GouradShading
  - MeshDepthMaterial:  no shading parameter in material, uses own specific shading
  - MeshBasicMaterial: no shading parameter in material, uses own specific shading
  - MeshLambertMaterial: FlatShading, GouraudShading [default]
  - MeshPhongMaterial: FlatShading, PhongShading [default]

Removed Loader.js from compiled lib
Fixed examples

CanvasRenderer/SVGRenderer: More code clean up and optimisations.

Changed the DepthMaterial to use this approach instead.

SubstractiveBlending ⟶ SubtractiveBlending

Implemented material blendings (THREE.NormalBlending, THREE.AdditiveBlending, THREE.SubtractiveBlending) in CanvasRenderer
Added MeshNormalMaterial (per face)

Cleaned up CanvasRenderer and SVGRenderer code a bit.

It's commented out, as it breaks shader validation in current Chrome :(.

There seems to be some bug in Chrome / ANGLE making it barf when using "gl_FragCoord" in fragment shader.

Curiously, while it breaks both 9.0.576.0 dev channel and latest continuous build 9.0.583.0, it does work fine in canary build with the same version as dev channel (9.0.576.0).

Go figure. Also in Firefox 4 beta 7 it works fine.

It seems there were some recent changes in handling of "gl_FragCoord" on Windows which probably broke something when fixing other bug:

http://code.google.com/p/chromium/issues/detail?id=59762
http://code.google.com/p/angleproject/issues/detail?id=71

TODO: make isolated test case and submit bug report (if this doesn't go away in next Chrome update).