Reagent state

Subscribes to any other reagent state changes and produce such events as items.

Syntax: reagent[`state;other_reagent]

o)r: reagent[`async];
o)// create reagent to receive r state notifications
o)s: reagent[`state;r];
o)react {[x:s] println["main State changed: \n%";x]};
o)close r;
main State changed:
id     | 12
message| Custom { kind: BrokenPipe, error: "closed" }
o)