add API for creating objects

[frnsys]

as part of the floor plan? you lay out an object as ids, e.g.:

1,1,1,1,1,1,A,A,1
1,1,1,1,1,1,A,1,1
1,1,1,1,1,1,1,1,1

where A is the plan of the object.

separately, you can map it to tags and properties, e.g.

world.setObjects({
  A: {
    props: {...},
    tags: [...]
  }
})