Remove avian dependency

[kristoff3r]

No description provided.

[TheNeikos]

Looking good!

[viridia]

I noticed a few things that I'd change, but I don't think we should block this PR for them:

• Angular damping can be a constant (rather than a component) since it only applies to the player.
• It would be nice if novices didn't have to mess with quaternions. A simple euclidean modulo should be sufficient.
• For collisions, it would simplify the example if all of the objects were modeled as circles, so that collisions are merely a function of euclidean distance between centers.

However, these items move us farther from Avian in the interest of simplicity; if the goal is to provide something that shows a path towards using Avian then these simplifications might not be appropriate.

[kristoff3r]

I noticed a few things that I'd change, but I don't think we should block this PR for them:

* Angular damping can be a constant (rather than a component) since it only applies to the player.

* It would be nice if novices didn't have to mess with quaternions. A simple euclidean modulo should be sufficient.

* For collisions, it would simplify the example if all of the objects were modeled as circles, so that collisions are merely a function of euclidean distance between centers.

However, these items move us farther from Avian in the interest of simplicity; if the goal is to provide something that shows a path towards using Avian then these simplifications might not be appropriate.

I changed the colliders to be circles, but this will require a bunch of more work even without the improvements you suggested:

• The later chapters need to be reworked to work without avian.
• We need to decide how many features can be introduced at this point, and potentially change the order of chapters. For example the code currently uses observers for collisions, but they are introduced later. Another option is to have multiple crates here that shows the code after certain points (as a replacement for the branches).