Created:
  new file lib/prediction_io/async_methods.rb as an abstraction for methods
  such as aget, adelete, acreate.

Added/Tested:
  PredictionIO::Connection
  - every request made includes pio_appkey now.

Added:
  - appkey to prediction_io.yml

Modified
  - features/support/env.rb to match new url, as each requests
  includes pio_appkey.