This commit provides a new join implementation that can join
tables with different group keys. It also implements a strategy
for evicting stale data from the join operation's cache when
it can be determined that a table will no longer be joined.
Currently early table eviction from the buffers of the join occurs
when the left-most group key column of both input streams are equal
and that column is part of the join key.
This modifies the `MultiResultDecoder` interface to accept an
`io.ReadCloser` so the `ResultIterator` can close the `io.Reader`
instead of doing it through a defer call. It then makes it so the
`Cancel()` method will close the reader or the reader will be
automatically closed when `More()` returns false.
In order to facilitate this change the query.PartitionKey
interface was changed to use the values.Value interface.
Additionally map was previously broken when it needed to repartition.
Tests have been added.
jlapacik
Nathaniel Cook
Jonathan A. Sternberg
Adam