Assets support

[czyzby]

• Global AssetManager container.
• Strongly-typed utility functions for easy asset loading.
• AssetDescriptor building utilities.
• Easy conversion of strings to FileHandle instances (an alternative to a rather obscure Gdx.files.internal and so on).
• Disposable utilities.
• Pool utilities.
• Unit tests.
  • Disposable.
  • Pool.
  • Asset loading.
  • FileHandle.

[czyzby]

@kotcrab I'd appreciate your input on this module. Do you think that batch asset loading operations make sense? For example, you could schedule loading of multiple textures with loadAll<Texture>("1.png", "2.png"). It might require some extra work and I'm wondering if its worth the effort - type-safe asset enums (as mentioned in the README) seem like a better solution and would come with trivial batching operations out of the box.

[kotcrab]

I think loadAll isn't worth it, it wouldn't even be able to return wrapper like load so later you would have to use asset to access them one by one, enums is better approach here and less error prone.

[czyzby]

Well, we could return a special implementation of the same wrapper storing <Array<Texture>> for example, but I agree that it might not be worth it.