Reserved aggregation names

NEST uses a heuristics based parser to parse the aggregations back in to typed responses. Because of this, some of the key properties we use to make decisions about parsing are not allowed as key names for aggregations in a request.

Elasticsearch 5.x will at some point get a flag that returns the aggregations in a parsable fashion. when this happens, this limitation will be lifted but until that time, avoid the following names for aggregation keys:

new []
{
    "score",
    "value_as_string",
    "keys",
    "max_score"
}