Updated the params_to_dict() method to be more efficient.
Added the ability to mass edit records. GitHub #427

While it was possible to update several records in one API call, pyrax
never exposed that ability. This commit adds the 'update_records()'
method to both the client and domain classes. It accepts a list of
dicts, where each dict represents a record and the values to be updated.
Merge branch 'working' of github.com:rackspace/pyrax into working