Jagged scrolling fix

This request merges [this commit](https://github.com/Arcnor/pixel-dungeon-gdx/commit/1587a47) to fix [this issue](https://github.com/Arcnor/pixel-dungeon-gdx/issues/57), and brings this repo up to date with the [upstream pixel-dungeon-gdx repo](https://github.com/Arcnor/pixel-dungeon-gdx) aside from iOS-related changes.