Add support for Bevy ECS

[BlockOG]

It would be nice to have the event system use Bevy systems, so it's easy to use it in Bevy games.

[lemunozm]

Hi! Is this event system something message-io should implement in this crate as part of it, or should it be a plugin/wrapper (maybe in another project) that allows message-io to work with Bevy and offer that event system?

[BlockOG]

Could be a plugin, maybe a system, just something that would allow for integration in Bevy.

[lemunozm]

I like the idea, but I think it doesn't belong to the message-io project itself. It think it should be another project that wraps this and makes this join.