1.0.0

* change `pageview` method to `page`
* add call to `page` as mandatory to initialize some analytics tools
* remove ability to `initialize` by `key`
* add checking for an integration already being loaded before loading
* add `#use` method for plugins
* add event emitter to `analytics`
* move integrations to [`analytics.js-integrations`](https://github.com/segmentio/analytics.js-integrations)
* add debugging to all integrations
* move integration factory to [`analytics.js-integration`](https://github.com/segmentio/analytics.js-integration)
* Amplitude: rename `pageview` option to `trackAllPages`
* Amplitude: add `trackNamedPages` option
* Google Analytics: add `trackNamedPages` option
* Google Analytics: remove `initialPageview` option
* Keen IO: rename `pageview` option to `trackAllPages`
* Keen IO: add `trackNamedPages` option
* Keen IO: remove `initialPageview` option
* Lytics: remove `initialPageview` option
* Mixpanel: rename `pageview` option to `trackAllPages`
* Mixpanel: add `trackNamedPages` option
* Mixpanel: remove `initialPageview` option
* Olark: rename `pageview` option  to `page`
* Tapstream: remove `initialPageview` option
* Tapstream: add `trackAllPages` option
* Tapstream: add `trackNamedPages` option
* Trak.io: remove `pageview` option
* Trak.io: remove `initialPageview` option
* Trak.io: add `trackNamedPages` option
* Woopra: remove `initialPageview` option