Improvements to how and what is stored in the texture caches. (#3834) ...

* Improvements to how and what is stored in the texture caches.
Built upon the good work from https://github.com/pixijs/pixi.js/pull/3789
+ For Text, the base textures were in the BaseTextureCache, but textures weren't in the TextureCache. This has been fixed
+ Now able to tell the BaseTexture the origin of where the canvas being passed through has come from. ie. was it from the text class? was it from the graphic class? was it from caching as a bitmap? More information now to track where these canvases (canvii??) have been generated from
+ BaseTexture has addBaseTextureToCache and removeBaseTextureFromCache functions, to match regular Texture. Any adding or removing to the BaseTextureCache is now through these functions

! Breaking change. When you call Texture.fromTextureFromCache - it no longer automatically removes it's base texture from the base texture cache. Not sure how people feel about this

? I don't like lines 233 to 236 in Texture.js, and line 591 in BaseTexture.js - I don't see why they are there or why they are needed, but I chickened out on removing them!

* Renaming function to more generic names

* Adding deprecation layer

* Fixed trying to add texture to BaseTexture cache causing unit test fail

* Fixed reading from the wrong cache

* Able to remove textures and base textures from their caches via object instances
Added debug warning if trying to add a texture to a cache id that already exists
Added unit tests

* Default string for texture origin

* Different object creation style

* textureCacheId is now an array of potential entries

* textureCacheId changed to textureCacheIds

* Removed unneeded string creation

Support that cache Sprite as Bitmap directly. (#3855) ...

* Cache Sprite as Bitmap directly.

In the current pixi.js , when we want to cache a sprite as Bitmap, we have to put the sprite add to a container , like this : 
```
var texture = PIXI.Texture.from(img);
var container = new PIXI.Container();
var sprite = new PIXI.Sprite(texture);
sprite.cacheAsBitmap = true;
container.addChild(sprite);
var renderTexture = PIXI.RenderTexture.create(sprite.width, sprite.height);
renderer.render(container, renderTexture);
```

With this PR , use could cache the sprite directly : 
```
var texture = PIXI.Texture.from(img);
var sprite = new PIXI.Sprite(texture);
sprite.cacheAsBitmap = true;
var renderTexture = PIXI.RenderTexture.create(sprite.width, sprite.height);
renderer.render(sprite, renderTexture);
```

* Update cacheAsBitmap.js

@sivael's fix for cacheAsBitmap is leaking objects #3801

Doc update (#3661)

Bugfix for #3356 and #3485 (#3494) ...

https://github.com/pixijs/pixi.js/pull/3366
^ This PR is wrong, it takes into the accountonly one of the two situations. 

After changing from worldTransform to localTransform, caching is proper for all cases.

Huge refactor to match a new shiny eslint file.

Prefer const (#3002) ...

* 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

Manually merge #2970

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`

fixes #2915

fixes #2910

Fix invalid hit-testing within containers cached as bitmaps. [#2895] (#2896)

fixes #2883

fix for static cacheAsBitmap

fixes for cacheAsBitmap

a better fix for cahceAsBitmap destroy

fixed cacheAsBitmap destroy bug

tweaked cacheAsBitmap ...

fixed issue with masks and filters + cacheAsBitmap interaction
also refactored a little to have use a CacheData that means we lower
the memory footprint of displayObjects a little.

fixed static cacheAsBitmap

Replaced core.math with core, resolves #2575

#2506 JiDW found a bug

More JSDoc fixes.

added generate texture to system renderer

refactored canvas ...

cacheAsBitmap
renderTexture

fixing up render texture

fixed cacheAsBitmap rendering

Changed help in cacheAsBitmap.js from "To remove simply set this property to 'null'" into "To remove simply set this property to 'false'".

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