More efficient JSON query result format.
This depends on https://github.com/prometheus/client_golang/pull/51.
For vectors, the result format looks like this:
```json
{
"version": 1,
"type" : "vector",
"value" : [
{
"timestamp" : 1421765411.045,
"value" : "65.475000",
"metric" : {
"quantile" : "0.5",
"instance" : "http://localhost:9090/metrics",
"job" : "prometheus",
"__name__" : "http_request_duration_microseconds",
"handler" : "/static/",
"method" : "get",
"code" : "304"
}
},
{
"timestamp" : 1421765411.045,
"value" : "5826.339000",
"metric" : {
"quantile" : "0.9",
"instance" : "http://localhost:9090/metrics",
"job" : "prometheus",
"__name__" : "http_request_duration_microseconds",
"handler" : "prometheus",
"method" : "get",
"code" : "200"
}
},
/* ... */
]
}
```
For matrices, it looks like this:
```json
{
"version": 1,
"type" : "matrix",
"value" : [
{
"metric" : {
"quantile" : "0.99",
"instance" : "http://localhost:9090/metrics",
"job" : "prometheus",
"__name__" : "http_request_duration_microseconds",
"handler" : "/static/",
"method" : "get",
"code" : "200"
},
"values" : [
[
1421765547.659,
"29162.953000"
],
[
1421765548.659,
"29162.953000"
],
[
1421765549.659,
"29162.953000"
],
/* ... */
]
}
]
}
```
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