Update what's new.md

dist/preview release/what's new.md

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 - SpritePackedManager extends SpriteManager so that a sprite sheet with different size sprites can be used ([JohnK](https://github.com/BabylonJSGuide))
 - MultiPickSprite and multiPickSpriteWithRay added to sprites ([JohnK](https://github.com/BabylonJSGuide))
+- SpritePackedManager support for JSON Objects that where not stringified, of with the frames parameter accepting Objects and Arrays ([Pryme8](https://github.com/Pryme8))
+- Added `SpriteMap` for creation of grid-based dynamically animated sprite atlas rendering (Beta) ([Pryme8](https://github.com/Pryme8))
 
 ### WebXR / WebVR