Implement publishLast

[benlesh]

Now that we have AsyncSubject #850, we need to add publishLast.

It's basically just:

import {multicast} from './multicast';
import {AsyncSubject} from '../subject/AsyncSubject';

export function publishLast() {
  return mutlicast.call(this, new AsyncSubject());
}

[kwonoj]

I'll give it a try on this.

[lock]

This thread has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs.