Character-tracking entity for easier camera controller integration

[idanarye]

If a camera tries to track the player directly, the tiny jittering of the floating capsule model will get amplified to the point of noticeablity when they get transferred to the camera. Smoothing can help, but the third party camera plugin may not support smoothing.

Tnua can and should help with that. It can provide a mechanism for adding a third entity that track the character but uses knowledge from Tnua to overcome the jittering and stabilize it (e.g. - keep at ground height when jumping). The camera (and maybe other things?) can then track that entity instead of the character entity directly.

[thomasza92]

Great work on this! I am new to using Bevy and this has been a great way for me to get a good character controller up and running. I would love for examples on how to use different cameras and having a dolly type camera working with Tnua in the future would be awesome!