Add support for perfect audience ecommerce params

Would potentially close #406 

But this needs careful review and attention, seeing as its my first, and most likely does not have sufficient tests. (edit: they failed ;p)
 
Would love to go over my thinking in person with one/more of you tomorrow. @ianstormtaylor @reinpk @calvinfo @lancejpollard 
Thanks guys. You're the coolest for helping me on this.

I'm going to attempt a total rewrite of this integration with their async
api:
http://support.perfectaudience.com/knowledgebase/articles/212490-visitor-tracking-api

Using the window._pq object. Any objections?

On Wed, Sep 10, 2014 at 6:10 PM, Lance Pollard <notifications@github.com>
wrote:

> In lib/perfect-audience/index.js:
>
> > +
> > +/**
> > + * Viewed Product.
> > + *
> > + * http://support.perfectaudience.com/knowledgebase/articles/211506-step-1-install-the-site-tracking-tag
> > + *
> > + * @param {Track} event
> > + */
> > +
> > +PerfectAudience.prototype.viewedProduct = function(track){
> > +  var total = track.total() || track.revenue();
> > +  var orderId = track.orderId();
> > +  var product = track.sku()
> > +  window._pa.orderId = orderId;
> > +  window._pa.revenue = total;
> > +  window._pa.productId= product;
>
> Yeah can are you able to see it in the browser make the call? I guess that
> is the only real way to confirm that it can reupdate.
>
> —
> Reply to this email directly or view it on GitHub
> <https://github.com/segmentio/analytics.js-integrations/pull/407/files#r17399379>
> .
>