add link-walking support

[reiddraper]

We need a way to add links to an object, and to query them

; starts with a bucket/key
; and then a list of bucket/link-tags
; specs
(link-walk conn "bucket" "key"
  [("other-bucket" "tag1" :keep true)
   ("second-bucket" "tag2")])

[bretthoerner]

As with mapreduce I only wonder if the containing vector is necessary, otherwise looks good.

[jmshoffs0812]

Thinking of something like this in sumo.client/put:

{:content-type "application/json"
 :value {:foo "bar" :baz "quux"}
 :links [{:bucket "b" :key "k0" :tag "t"}
         {:bucket "b" :key "k1" :tag "t"}]}

[reiddraper]

Thinking of something like this in sumo.client/put:

+1