* special purpose materials.

* rename example from special_purpose -> channels.  Add camera controls.

* minor polish to webgl_materials_channels.

* add standard material with displacement, normal and ao to show contract with normal and depth materials.

* fix orthographic camera near/far bounds.

* remove double add of material_channels example.

* Implemented user-defined clipping planes.

* Renderer: Minor documentation update.

* Implements object-level clipping.

* Renderer: Minor cosmetic changes.

* Fixed lethal typo in normal shader.

* Let shadows respect .side of object's material.

* Fixed Plane.applyMatrix4.

- Scale denormalized but did not scale the position
- Projection is not supported (solved by documentation)
- Removed unnecessary copying to make up for the normalization
- Still arguably too heavy

* Added custom clipping example.

* Clipping: Fixed transition to disabled state.

* Improved custom clipping example.

- GUI dependency of volume visualization on Enabled state
- Larger radius for cylindrical global clipping area

* No .matrixAutoUpdate = false in clipping example.

* Let ShadowMap check renderer.localClippingEnabled.

* Added a simplified clipping example.

adds both new spotlight examples