Added OBJ converter test example.

Modified Three.js to handle converted models:

 - extended WebGL renderer to use texturing
   - broke down model into multiple VBOs according to materials
   - textures are lazy created when images get loaded
     (converter takes care of resizing images to nearest power of 2
      dimensions using 2d canvas)

 - changed material array semantics in Mesh object
    - before: multiple materials were applied to all faces (broken in WebGL, needs multitexturing shader)
    - now: there is only single material per face, but one mesh can have faces with different materials

 - added per vertex normals (to get smooth shading in WebGL)

* `CanvasRenderer` and `SVGRenderer` basic lighting support (`*ColorStroke`/`*ColorFill` only)
* `Renderer` > `Projector`. `CanvasRenderer`, `SVGRenderer` and `DOMRenderer` do not extend anymore
* Interactivity base code (hdi folder). To be refactored... ([mindlapse](http://github.com/mindlapse))
* Added `computeCentroids` method to `Geometry`
* Included `Stats.js` directly in the `/examples` folder to avoid the need of internet for playing around

Using projection * view * obj matrix to transform vertices in Renderer instead of transforming twice (once by view * obj and once by projection).

  * Added getCenter to Face4

- Minor tweaks

 * Bug Fix: Matrix4.makeInvert was calling a non existent scale method. Replaced with multiplyScalar.
 * Bug Fix: DirectionalLight wasn't normalizing the direction vector.
 * Added lights to the scene for test.html

 * Add lighting code in the scene rendering loop

 * Added float precision in shader code to shaders compile now.
 * Changed occurrences of WebGL typed Arrays and UnsignedShort typed arrays to new array types

* Additional `Matrix4` and `Vector3` methods

- Camelcased the minified files (it feels weird both ways anyway...)

- Face4 with MeshBitmapMaterial gap fixed

- `three_debug.js` checks for broken UVs and display these faces with pink color instead