Makes the code so much nicer imho...

use switch statements in Vector2/3/4.getComponents()/setComponents() based on it being 5-10x faster than index-to-name based on benchmark_vector3components.html

inline Vector2/3/4/Quaternion.length()/lengthSq() and optimize Vector2/3/4.setLength() with unit test coverage.

fixed #2728, Moved geometry primitives out of src/core into src/math.  src/core is now exclusive scene primitives.

Vector2: setX, setY, Vector4: setX, setY, setZ, equals.  Unit tests for Vector2, Vector3 and Vector4.

Also trying to make a bit nicer UVs for ExtrudeGeometry / TextGeometry.

Some clean up on Vector* constructors.
Added UV::clone.

reworked Vector classes, no change in API, reordered methods, divide-by-zero prevention, removed use of .set() in methods for better performance

I don't remember when was the last time I used them. Current Web Developer Tools do this already for you.

Color::updateRGBA ⟶ Color::updateRGB

- getters/setters are no more in Vector3
  - object hierarchies thus don't use "isDirty"
  - this was completely killing performance for anything that was touching a lot of Vector3 like creation of meshes and dynamic buffers
  - even without this, performance of hierarchies went up (a lot)

- objects do not get passed renderer anymore
  - camera was almost also removed, but this is useful for LOD (though there may be some cleaner way to do this?)

- material ids are now unified, this makes "geometry.sortFacesByMaterial" faster (thus scene init / GUI blocking is shorter)

- all WebGL examples should work now (render-to-texture has weird lights and in some camera control feels different)

- CanvasRender still broken, despite many efforts :(
   - currently only points and lines work, faces don't show up. I think this may need assistance from mrdoob.

Otherwise things are very much work in progress, expect everything to be broken.

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

* Minor fixes (Geometry normal calculation)
* Isolated Matrix3 code into `Matrix3.js`
* README and TODO updated

  * Added getCenter to Face4

* `Face4` now supports `MeshBitmapUVMappingMaterial`
* Changed order of `*StrokeMaterial` parameters. Now it's `color`, `opacity`, `lineWidth`.
* `BitmapUVMappingMaterial` > `MeshBitmapUVMappingMaterial`
* `ColorFillMaterial` > `MeshColorFillMaterial`
* `ColorStrokeMaterial` > `MeshColorStrokeMaterial`
* `FaceColorFillMaterial` > `MeshFaceColorFillMaterial`
* `FaceColorStrokeMaterial` > `MeshFaceColorStrokeMaterial`
* `ColorStrokeMaterial` > `LineColorMaterial`
* `Rectangle.instersects` returned false with rectangles with 0px witdh or height