Initial denominator formula

reworked and rebased from issue #18441

Denominator manages DNS entries in cloud providers like Amazon, Rackspace, UltraDNS, and DynECT.

Ex. the following will add a record pointing to your current EC2 node's IP address
```
$ denominator -p route53 record -z myzone.com. add -n wonky.myzone.com. -t A --ec2-public-ipv4
;; in zone myzone.com. adding to rrset wonky.myzone.com. A values: [{address=75.101.168.33}]
;; ok
```