Add support for .world files in tmxrasterizer

[RainingChain]

With this PR, users will be able to convert a .world file into a .png file by running the command :
tmxrasterizer [options...]

This PR does not affect .tmx/.json conversion to png.

[bjorn]

Great patch overal! I only had minor comments, which I have put inline.

[bjorn]

@RainingChain You seem to have marked all my comments as resolved, but have not pushed a new version of your commit. Did you forget?

[RainingChain]

@RainingChain You seem to have marked all my comments as resolved, but have not pushed a new version of your commit. Did you forget?

My PR has a bug because the width of maps is not initialized upon calling WorldManager::privateLoadWorld().

I think I'll just calculate the correct map size in TmxRasterizer::renderWorld().

[bjorn]

@RainingChain If you push your updated commit I can also see if I can help with that. I think the easiest would be to load each map and rely on MapRenderer::mapBoundingRect. I hope that tileset caching can ensure that this won't add too much of a performance hit.

[RainingChain]

I fixed the map boundaries bug and made the changes you requested.

[bjorn]

@RainingChain Thanks a lot!