Fix NullPointerException when reading from S3
Use ImmutableEnumSet
Fix use of closed RecordReader
Introduce Signature object for functions
Refactor LocalExecutionPlanner

Replace Multimap with Map, now that all our channels contain only a
single symbol
Add unit test for DISTINCT aggregation on a JOIN
Add catalog and schema to jdbc string
Add documentation for JDBC driver
Add 0.57 release notes
Update snapshot dependencies
[maven-release-plugin] prepare release 0.57
[maven-release-plugin] prepare for next development iteration
Load balance split assignment across queries