Add method for adding users to a custom audience, using the post-October 2014 API.
Merge pull request #38 from GallopLabs/add-users-to-audience

Add method for adding users to a custom audience, using the post-October 2014 API.
Add method for adding users to a custom audience.
Merge remote-tracking branch 'upstream/master' into cleanup-deprecated
Revert "Delete "create_audience_from_website" since with the present API, it no longer does anything different than other audiences."

This reverts commit 653fd4518eb5916946ff0c21be589700b1978828.