`Ember.computed.sum` takes a single property that is an array (see [here](https://github.com/emberjs/ember.js/blob/master/packages_es6/ember-runtime/lib/computed/reduce_computed_macros.js)) that gets summed up.

This macro multiplies two values (from properties).  I personally am unsure of the need to multiply an array of items. I would be happy to add another macro that multiplies all items in a given dependent key (which is an array), and another that multiplies all items out of an array of objects (essentially like `Ember.computed.sum` and `EmberCPM.Macros.sumBy`), but would need help on naming.

The three macros we are talking about:

* a macro that multiplies all items in a dependent key that is an array (ala `[1,2,3,4]` would equal 24)
* a macro that multiplies a specific property from each item in an array of objects (ala `[{i:1}, {i:2}, {i:3}, {i:4}]`)
* a macro that multiplies all properties that are specified as strings to the macro (ala `'prop1','prop2','prop3','prop4'`)

I *might* be able to make one macro do all of those things, but it would not be a simple one...