* Fixes an issue when destroying ticker on callback

* Handles more cases when destroying

* Adds ticker priority

* Removes EventEmitter dependency from ticker

* Small optimization to avoid Function.call

* Changes ticker priority with UPDATE_PRIORITY const

* Fixes linting

* Use a linked list approach to ticker listeners

* Oops fixes test

* Minor fixes

* Removes unnecessary destroy check

* Minor optimizations

* Adds memory clean-up to Ticker

* Updated documentation

* Rename local `last` to `previous`

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

Discovered that using this kind of code:

```const { MY_SETTING } from settings;```

means that changing settings properties has no effect as the objects
are being set before the user changes them.

* Made const that are setting writable

* Moved more items to the settings

* added prefer-const rule to .eslintrc

* eslint const autofixes

* manual let to const changes; lint free;

* added brace style 'allman' to eslintrc

* brace style, comment fixes and default arg

* brace style fixes

* more brace styles

* Point default args

* Point brace styles

* Observable Point default args

* more brace styles

* jsdoc comment style

* brace style

* brace styles and small jsdoc fix

* brace styles

* removed unneeded eslint inline comment

* brace styles; lint free

* 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)

* 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

* Epic run through the docs

* Fixed merge issue

* PIXI.utils now outputs its documentation correctly

# Conflicts:
#	src/core/renderers/webgl/WebGLRenderer.js
#	src/core/sprites/webgl/SpriteRenderer.js
#	src/extract/canvas/CanvasExtract.js
#	src/extract/webgl/WebGLExtract.js

Issues fixed by these documentation updates:

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