Acceleration?
Pull out :turn-funcs into a list of behaviors.
Update the world in one go routine.

Conflicts:

	src/boids/core.cljs
Divide by zero bug.

Conflicts:

	src/boids/core.cljs
WIP: It is still slow. Why?

Memoize behavior functions?

Conflicts:

	src/boids/core.cljs
TODO
Merge branch 'master' of github.com:jwilner/boids