Breaking changes, API surface rewrite + enhanced e-commerce

This module started out as a simple project with an aim to abstract away the native side of the Google Analytics library. The hope was that we could have simple functions like trackScreenView, trackEvent, and developers wouldn't have to think about stuff like building "Hits" and dispatching them.

But as use-cases have become complex, the API of the module became messy. This release hopes to put that right.

The API should mostly be backwards-compatible, except those special use-cases. See this wiki post for more details.

This release also includes a more fully developed enhanced e-commerce, which lets you track even more product actions and impressions.