Change API JSON response format to include errors etc

[rgrp]

Move to a format that has a separate responseHeader and response.

A standard package response

{
  responseHeader: {
    status: 0,
  }    
  response: {package-dict}
}

On error:

{
  responseHeader: {
    status: {err-code},
    error: 'message'
  }    
  response: none
}

A search query

Based directly on solr.

{
  responseHeader: {
    status: 0,
  }    
  response: {
    numFound: 5,
    start: 0
    docs: [
    ]
  }
}

Issues

This is a breaking change for clients

References

• ​http://wiki.apache.org/solr/SolJSON
• ​http://www.flickr.com/services/api/response.json.html