Various Math improvements from Clara.io

add docs per @WestLangley's request: https://github.com/mrdoob/three.js/pull/5788#issuecomment-67857995

remove Matrix4.makeShear per @WestLangley here: https://github.com/mrdoob/three.js/pull/5788#issuecomment-67852744

editor: add fullscreen mode

Fix x4121 warnings

- Fix warning X4121: gradient-based operations must be moved out of flow
  control to prevent divergence. Performance may improve by using a non-gradient operation
- This is seen in Firefox Stable (34) on Windows
- This fix seems to give small amount of fps boost