Switch to ES6 Set

[gordonkristan]

We need to get rid of the cherry-picked Ember Set implementation and use the ES6 set instead.

[mtheoryx]

Just ran into an interesting issue possibly relating to this or issue #38 when trying out ember-graph latest.

We're using the withoutAll() method, but getting an error on ember 1.8.1 and the Oct 25th release of ember graph:

TypeError: existingBands.withoutAll is not a function

[gordonkristan]

It's been a long time so I can't remember exactly, but this might be because I'm no longer extending the built-in Set class. Because Ember.Set doesn't exist in Ember 2.0 anymore, I polyfill it to EmberGraph.Set and use that class instead. You can either switch to using EG.Set instead of Em.Set, or you can add this polyfill somewhere:

Ember.Set.reopen({
    withoutAll(items) {
        const ret = this.copy();
        ret.removeObjects(items);
        return ret;
    }
});

I think this behavior changed sometime in August, so to your point about the release process: we really need release notes. 😄