Fix DisplacementFilter when using multiple filters (#4560)

Read `texture` via `_texture` directly in sprite (#3780) ...

* Use `*._texture.*` directly in Sprite.js

It could offer a bit little performance gains.
And  read texture via `_texture` is a common way/style in  PIXI.js

* Update CanvasTinter.js

* Update DisplacementFilter.js

* Update Graphics.js

Fix #3609 , about `filterClamp` & `filterArea` (#3626) ...

* Fix : about filterArea & filterClamp

* Remove needless code

* cosmetice

Improved documentation ...

Class member documentation improved via removal of unnecessary @memberofs - more members now show up in the docs.
Class getter/setter documentation improved using technique above, and also by removing documentation for setters. Documentation was only showing the setter docs, whereas the getter is where the important information is. JSDoc maintainers themselves recommend just doccing the getter jsdoc3/jsdoc#973
Documented a few classes to let devs know that they are automatically created by PIXI and added to renderer.plugins, like interactionManager and prepare

Removes glslify

Huge refactor to match a new shiny eslint file.

some more es6 changes (#2969) ...

* some more es6 changes
- const instead of let if possible
- arrow functions
- string templates
- argument defaults

* object property shorthand

* some more es6 changes
- const instead of let if possible
- arrow functions
- string templates
- argument defaults

* Revert "Merge branch 'dev-es6-sb' of github.com:stbaer/pixi.js into dev-es6-sb"

This reverts commit 8d3af81, reversing
changes made to e8b9948.

* Revert "Merge branch 'dev-es6' into dev-es6-sb"

This reverts commit 3eeaf79, reversing
changes made to fb69536.

* Revert "Revert "Merge branch 'dev-es6-sb' of github.com:stbaer/pixi.js into dev-es6-sb""

This reverts commit c860228.

* fix RenderTexture, incomplete merge

* fix for text font properties

* reverted some changes

* checked out License, Readme and Contributinf from dev-es6

* editorconfig updated: 2 spaces for .eslintrc

* added eslint rule: spaces around fat arrow

* used eslint fix for consistent spaces around fat arrow

* don't allow scale.x or scale.y to be 0 in displayObject setTransform

* removed jshint comments (again)

Update imports and exports, getters and setters

Disallow the use of `var`

Implementing classes using the new ES6 syntax (#2936) ...

* Migration to ES6 classes

* Migration to ES6 classes

* Migration to ES6 classes

* Migration to ES6 classes

* Using babelify to transpile ES6 code

* Adding babel-preset-es2015 in devDependencies

filter tidy up part one ...

blur
pixelate
twist
displacement
colormatrix
void

filterClamp

fixed displacement attributes

separate Shader class

Updated and fixed JSDocs

first round to clean some jslint errors

production test fixes ...

fixed masking issue
fixed sprite batching issue
refactored displacement map
fixed renderTexture issue

fixed error in batcher ...

fixed bitmap font parser
added displacement map

added gray filter move old filters

Massive documentation update; fixes many issues. ...

Issues fixed by these documentation updates:

- #1973, fixed filter and BitmapText property docs
- #1908, fixed type reference links
- #1856, fixed name of MeshShader

remove unecessary warn log

Merge branch 'dev' of github.com:GoodBoyDigital/pixi.js into displacementShader

* Improved usability of displacement filter

Merge pull request #1915 from bchevalier/displacementShader ...

[Fix/Hack] Displacement filter blurry on iphone4, iphone4s and ipod5

Removed hack

Changed precision to medium in displacement fragment shader

Added hack to displacement filter shader to avoid pixelized effect on some devices

Depecrate `PIXI.math` namespace ...

Access math members from PIXI when outside of core, require the math module directly when inside of core.

more doc clean ups..

fixed extends doc issue