Nik Everett 16812cc032 Migrate moving_avg pipeline aggregation to NamedWriteable
This is the first pipeline aggregation that doesn't have its own
bucket type that needs serializing. It uses InternalHistogram instead.
So that required reworking the new-style `registerAggregation` method
to not require bucket readers. So I built `PipelineAggregationSpec` to
mirror `AggregationSpec`. It allows registering any number of bucket
readers or result readers.
2016-07-18 10:14:09 -04:00
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