Add eCommerce support

This PR does a few things:

* Adds eCommerce support (Fixes #17).  Specifically for WooCommerce and WP eCommerce.
* Prefixes filter names, functions names (and much else) with Segment, rather than Segment_IO
* Adds a fully baked page() method.
* Adds a class to help with client-side handling of server-side events.
* Features Bob Ross quotes in commit messages.
Sure.  If folks want to add that `displayName` parameter, I suppose they can now do so via the `segment_get_current_user_identify` filter.