Cli record add remove

for issue #11 

This allows the cli to add and remove records.  `--ttl` is optional on record add, and when it is specified, it will replace whatever the old ttl is on existing records.  

There's no impact if you remove a record already gone, or add one that already exists, unless you specify an updated `--ttl`.

Examples (keeping in mind mock is not durable)

Adding multiple records:
```
$ denominator -p mock record -z denominator.io. add -n www1.myzone.com. -t A -d 1.1.1.1 -d 1.1.1.2
;; in zone denominator.io. adding to rrset www1.myzone.com. A values: [{address=1.1.1.1},{address=1.1.1.2}]
;; ok
```

Adding a record and replacing ttl:
```
$ denominator -p mock record -z denominator.io. add -n www1.myzone.com. -t A --ttl 3600 -d 1.1.1.1
;; in zone denominator.io. adding to rrset www1.myzone.com. A values: [{address=1.1.1.1}] applying ttl 3600
;; ok
```

Removing  a record:
```
$ denominator -p mock record -z denominator.io. remove -n www1.myzone.com. -t A -d 1.1.1.1
;; in zone denominator.io. removing from rrset www1.myzone.com. A values: [{address=1.1.1.1}]
;; ok
```