Fix for #53 - add support for user_data to function droplet_new

Fixes #53

I did not check, if the region supports  "user_data" . This could be done by checking against the "metadata" feature of the region.

If not supported, the api call still works, as far as I remember. 

If an image really uses the user_data passed in cannot be verified automatically. But the call never fails, if not.