Support special rrset types in Route53 client

[exarkun]

#3 introduced support only for regular resource record sets. change_resource_record_sets and list_resource_record_sets should probably both know about some extra things to fully expose the Route53 functionality: http://docs.aws.amazon.com/Route53/latest/APIReference/API_ResourceRecordSet.html defines the schema for specifying things like "alias resource record sets" and "failover resource record sets" and so on.

I'm just filing one ticket for now but it probably makes sense to have one ticket per special rrset type.

[exarkun]

An intermediate step here might be to not blow up when encountering these other rrset types. Since they have different elements, they currently break list_resource_record_sets merely by existing. :/