add initial ecommerce

@ianstormtaylor, @DirtyAnalytics 

method name, regexp:

```js
['addedProduct', /added product/i]
['removedProduct', /removed product/i]
['viewedProduct', /viewed product/i]
['checkedout', /checked out/i]
```

i didn't go crazy and used `obj-case` because i don't want to promote users to go crazy with event names and "we'll take care of it", because i think they should follow the docs.

also `addedProduct` is kinda lame because camelcase is lame, so if you want them to be `added`, `removed`, `viewed` i'll be happy to change that, the reason i appended `product` is because we might use `added`, `removed` in the future.