This plugin is meant to have some add-ons to interact with the
simulation to provide insight.
This first change adds a cursor under the mouse with the intention that
it's circle can be used as a reticule for targeting boids. Hovering over
a cluster and getting their CoM or velocities, for example.
The examples and learning plugins have outlived their usefulness, and
this repo already has substantial history in being a boids plugin. I'm
renaming the crate (and repo, but that isn't visible to git) to treat
this simply as a boids repo.
I ignored the use of sound because I don't want to download sound files.
I'm not certain that the `steppings` module is required, but I don't
really know what it does, either.
