updating to spec 1.0

This commit includes a number of significant changes:

  - updating the library to use the new spec
  - moving to analytics.write_key API
  - moving to a consumer in a separate thread
  - adding request retries
  - python 3 support
  - making analytics.flush() synchronous
  - adding full travis tests
![selfie-0](http://i.imgur.com/1wAVMnU.gif)