Added 'unique' hash to make controlling DNS via web easier, added raise_for_status for #1

When dealing with an interface without a backing store, i.e. web enabled front-end using the route53 data, there is no way to identify the individual recordsets. I added an SHA hash to the _initial_set dictionary so that a reasonably unique key could be maintained for the second fetch during update.

I also added a raise_for_status to raise an exception if the API query fails to get a valid response which should address issue #1.