Add links to sub-resources and related actions in JSON responses.

[llvtt]

Addresses #47

Changes:

• Top-level links field in response gives available paths at the same level as the request.
• links fields within sub-documents describing resources give paths to actions on those resources.
• Make all non-empty responses from the server return valid JSON.

Documentation changes are in progress. Some example requests/responses are here: https://gist.github.com/lovett89/218bcac23e6c0ea52e41

[llvtt]

@craiggwilson Updated (gist in top comment updated, too).

Changes:

• Restrict the scope of links, so that links provide actions only on the immediate resource. A link to GET the parent resource is still provided.
• Add links to GET each sub-resource (e.g., shard, replica set member) when getting a parent resource.

[craiggwilson]

This looks excellent Luke. Great job!!! The output of all the links looks good, so I can sign off on that. A python guy might want to look at the actual python code.

[llvtt]

@behackett Updated.

[behackett]

LGTM