ArcadePhysics.World.separateCircle is a new method that handles all circular body collisions internally within Arcade Physics (thanks @VitaZheltyakov)
All of the Arcade Physics internal methods, such as `collideGroupVsSelf`, `collideSpriteVsSprite` and so on, have been updated to work with circular body shapes (thanks @VitaZheltyakov)
ArcadePhysics.Body.onWorldBounds is a new Signal that is dispatched whenever the Body collides with the world bounds, something that was previously difficult to detect. Due to the potentially high volume of signals this could create it is disabled by default. To use this feature set this property to a Phaser.Signal: `sprite.body.onWorldBounds = new Phaser.Signal()` and it will be called when a collision happens, passing one argument: the sprite on which it occurred.
* The PIXI.BaseTexture.imageUrl property has been removed, as it was never actually populated.
* The PIXI.BaseTexture._UID property has been removed, as it was never actually used internally.
* All references to PIXI.BaseTextureCache have been removed (primarily from BaseTexture.destroy and Texture.destroy), as the BaseTextureCache was never used internally by Phaser, or by our custom version of Pixi.
* PIXI.TextureCache has been removed. It was only ever used by the __default and __missing images that Phaser generates on start-up. It wasn't used internally by Phaser anywhere else, and the only references Pixi has to it have all been removed. If you need it in your own game, please refactor it to avoid it, or re-create the object on the PIXI global object.
* Canvases created by `BaseTexture.fromCanvas` no longer have the `_pixiId` property attached to them, as this was never used internally by Phaser or Pixi.
* PIXI.BaseTexture.updateSourceImage is now deprecated. Please use `Sprite.loadTexture` instead.
* The property PIXI.BaseTextureCacheIdGenerator has been removed, as it is no longer used internally by Phaser or Pixi.
* PIXI.Texture.addTextureToCache has been removed. The PIXI Texture Cache was never actually used by Phaser, and was leading to complications internally.
* PIXI.Texture.removeTextureFromCache has been removed. The PIXI Texture Cache was never actually used by Phaser, and was leading to complications internally.
* PIXI.Texture.fromFrame and PIXI.Sprite.fromFrame have been removed. They relied on the PIXI Texture Cache, which was never actually used by Phaser, and was never used internally by Pixi either.
* The property PIXI.TextureCacheIdGenerator has been removed, as it was not used internally.
* The property PIXI.FrameCache has been removed, as it was not used internally.
* The missing image texture, for when an image has failed to load, is now available under `Phaser.Cache.MISSING`.
* Phaser.Cache.addImage will now check the key given, and if `__default` or `__missing` it will update the new consts `Phaser.Cache.DEFAULT` and `Phaser.Cache.MISSING` accordingly, allowing you to replace the default or missing image textures used by Phaser.
* Phaser.Cache.getPixiTexture has now been removed, as the Pixi Cache isn't used internally anywhere any longer.
* Phaser.Cache.getPixiBaseTexture has now been removed, as the Pixi Cache isn't used internally anywhere any longer.
Graphics objects enabled for input would fail to do anything if a Phaser Polygon was given to the Graphics object (which it was in nearly all cases), as it wouldn't detect input correctly with flattened polygons (thanks @symbiane #2591)
PIXI.Tilemap - _renderBatch using a local 'degenerate' flag to signal to next iteration that one should be inserted before the next triangle.
Phaser.TilemapLayerGL - add degenerate markers at end of rows and whenever a row has a break in it (e.g. empty tiles)
Phaser.Tileset - new addDegenerate function which prevents double markers in a row
Phaser.Tilemap now creates internal map layers for each tileset except the first one (which will be handled by the createLayer call from the game). It also stores a reference to each tileset where the new map layers can access it.
Phaser.TilemapLayerGL uses the new tileset reference to ensure the correct base image and tile sizes are used for each new layer.
PIXI.Tilemap: added initialisation of glBatch to null in c'tor.
Phaser.TilemapParser was cleaned up to remove the now unnecessary tilemap parameter and the attempt to create layers while parsing.
