Merge pull request #5170 from jahting/pnltrixmpl

PnlTri.js Rev. 2.0: now handles vertices and edges on other edges (co-linearity)
Mesh raycast() returning new Face3( a, b, c, normal ) instead of [ a, b, c ] array. See #5164.
BufferAttribute: Added copyAt() to simplify item copying. (Not sure about naming)
Updated interactive buffergeometry example.
Updated builds.
Implemented @pixelnerve's changes.
Fixed 'clear' method's description

WebGLRenderer's documentation incorrectly stated that if no parameters were passed to it, the 'clear' method will not clear any buffers. The default behaviour is in fact the opposite: if an argument is undefined, the corresponding buffer will be cleared. The document now correctly describes the default behaviour.
Source code of the method: https://github.com/mrdoob/three.js/blob/master/src/renderers/WebGLRenderer.js#L368
Merge pull request #5174 from abiro/dev

Fixed 'WebGLRenderer.clear' method's description
Update ArrowHelper.html
Merge pull request #5177 from yatesjdy/patch-1

Update ArrowHelper.html
reverse animation with negative timeScale
Merge branch 'add-reverse-animation' of https://github.com/oxyflour/three.js into dev
Docs: Updated Material.overdraw description. Fixes #5176.
UI: Added textAlign.
Fixed decals example order.
Update Scene.html

it's -> its
Merge pull request #5191 from Kiloblargh/patch-1

Update Scene.html
Support BufferGeometry in Box3.setFromObject()
Improved some examples.
Improved decal example.