fixed some filter issues with textures not clearing correctly (#3525) ...

* fixed some filter issues with textures not clearing correctly

* removed commented code

* added a clear to the correct place (when filters are stacked)

Add clear method to CanvasRenderer (#3423) ...

* Add clear method to CanvasRenderer

WebGLRenderer has the ```clear``` method , I think CanvasRenderer should has it too.

Sometimes, maybe we want to clear the canvas manually via ``` game.renderer.clear()``` .

If  CanvasRenderer doesn't  has this method ,  there will be an error.

* Update CanvasRenderer.js

Protect the initial state of `this._activeRenderTarget` in _indexContext (#3443) ...

* Update WebGLRenderer.js

```
    this._activeRenderTarget = null;
    this._activeTextureLocation = 999;
    this._activeTexture = null;
````
must before `this._indexContext()` , otherwise  the _activeRenderTarget & _activeTexture init in  _indexContext will back to `null`.

* Add a blank line for cosmetic.

Do not unload generated textures when manually running the texture garbage collector. This already happens when it is run automatically, as it will cause the texture to not be able to be renderered again (#3342)

Fixed createColoredCanvas() documentation ...

createColoredCanvas() was documented as taking a number, but should have
said it takes a string.

fixed settings not being respected (#3315) ...

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.

add additional prepare and gc settings (#3305)

Merge pull request #3300 from pixijs/fix-jsdocs ...

Fixes jsdoc issues with exports and module.exports

Moves constants that are actually settings (#3298) ...

* Made const that are setting writable

* Moved more items to the settings

Merge pull request #3289 from pixijs/lib-dist-builds ...

Build System, Babel and ES6 src

Fixes jsdoc issues with exports and module.exports

Add jsdoc for Filter.uniforms

little filter-fix (#3295) ...

* little filter-fix

* removed space

Merge pull request #3206 from pixijs/dev-vao-state-cache ...

Dev vao state cache

Removes glslify

spelling

Cache VAO states

Reduce redundant texture binds (#3258)

Merge branch 'master' into dev

minor eslint fixes

Merge pull request #3189 from gameofbombs/dev4 ...

Canvas stuff

Dev texture states cacheing (#3201) ...

* minimal texture bounds pass 1

* cheeky opts

* tidy up code

* create empty textures

* added empty texture

* couple more tweaks

* fixed empty texture issue

* fixed tweaked so id's sit on glTexture

means it should work on multiple contexts

* tweaked unbound textures

* tidy up

* upped max textures to 4 for mobile!

also sending state to tiling sprite VAO

* removed _activeTetureLocation

* tweaked eslint

* make sure buffer is bound

* updates based on @englercj review points

- Added vertexCount back in as it still yields much faster results in
iOS
- Tidied old comments
- Replaced i++ with ++i

BlendMode canvas fix

Fix crash of DropShadow filter (#3162)

fix #1841 by defaults system renderer resolution

use objects where we map render context ids

Restore lost context before using it; fixes #2958 ...

Looks like since we call loseContext() on `WebGLRenderer#destroy()` that
if you create another WebGLRenderer with the same canvas the browser will
recycle that lost context and return it.

This means when we try to use the context it is actually in a lost state.
This change tries to restore a lost context before we use it. It also adds
a debug assert at one location that will be invalid if the context is
invalid.

Fix #2971; merges #3046

strange imports problem

updated some doc comments (#3038)