Emulate slope-scaled depth bias on WebGL 1 (playcanvas#913)

* emulate slope-scaled depth bias on WebGL 1
* fix formula
* fix vsm

Merge pull request playcanvas#903 from willeastcott/master

Update to scripts 2.0

fix docs compile error

Fix flappy bird project image.

Replace call to unbind with off

Fix android detection

README example to be full html file, and get rid off tabs all around

Merge pull request playcanvas#860 from playcanvas/renaming-orientated…

…-box

Renamed pc.OrientatedBox to pc.OrientedBox

Merge branch 'master' of github.com:playcanvas/engine

Updated renderNextFrame docs