New World class with bound methods.

[HexDecimal]

I quickly put this together as an example, although I might end up using this unironically for the moment.

No tests yet and serialization functions would need to be moved to prevent a cyclic import.

This resolves #1 since you can't accidentally use the implicit world when using this class.

[slavfox]

LGTM, although I'm partial to ripping the ecs module out into World methods entirely for snecs 2.0 rather than adding alternate ways to use the library.

[HexDecimal]

That could be done, it's a bit more work though.

I also haven't yet looked into the performance differences between this and the existing API. I should add benchmarks for this sometime.