code: function make(o) {
    if (is(o)) return o;
    var u = get(o);
    if (!u) {
      u = _make(o);
      set.add(u);
      upwardifieds.set(o, u);
    }
    return u;
  }
docs: ## make
  
  Constructor for upwardable object.
  Default export from this module, often imported as `makeUpwardableObject`,
  and aliased as `U` in `index.js`.