Use an ECS

[rosalogia]

It's becoming increasingly difficult to manage the moving parts of the project without a way to conveniently say "well, all these things move in one of four directions so share this code between them, and all these things have health and take damage so share that code between them, ..."

A good solution to this problem is introducing an Entity-Component-System library, some good choices may be Legion or Specs. Legion is more up to date than Specs, but Specs is slightly more documented (in that there is a Specs book). Alternatively, we could roll our own, but we should figure out whether there's any real benefit to that before we decide to do so.