Simple animations for movement

[bdjewkes]

A few people have expressed that movement is confusing on the client because it doesn't render interpolations between snapshots of the state.

I think that the simplest implementation of doing this would be to animate a linear interpolation ('lerp') over several frames of all entities whose positions have changed.

This will breakdown if we introduce types of movement that shouldn't be linear (like a teleport), but I think it'd be a good place to start.