Doc value Fields

Allows to return the doc value representation of a field for each hit, for example:

GET /_search
{
    "query" : {
        "match_all": {}
    },
    "docvalue_fields" : ["test1", "test2"]
}

Doc value fields can work on fields that are not stored.

Note that if the fields parameter specifies fields without docvalues it will try to load the value from the fielddata cache causing the terms for that field to be loaded to memory (cached), which will result in more memory consumption.