Render tilemap when camera outside of world bounds, layer wrapping

Prior to this change, TilemapLayers always restricted themselves to
rendering strictly within the world bounds. If the camera was allowed
to go beyond the world bounds, then the tilemap would appear to stop
scrolling once the camera hit the world edge. This allows the tilemap
to continue scrolling, showing empty space beyond the edge of the map.

Additionally, when the new "wrap" parameter is true, the tilemap will
render its opposite edge in the empty space. This simulates the map as
if it was the surface of a toroid (donut) rather than a flat plane.
Merge pull request #851 from jotson/dev

Render tilemap when camera outside of world bounds, layer wrapping