Implement arbitrary aggregation function
Fix an issue when using row_number() and limit() together
Fixed a minor issue with the 0.80 release notes
Fix coercion for variable arity functions

Arguments were not being coerced if the first argument was not a super
type of the later arguments.
Implemented LEAST function with variable number of arguments.
Add docs for arbitrary() and release notes for 0.88
Minor cleanup of Least

Remove custom method in Signatures to create a specialized signature for least.
That's not necessary outside of the Least class and it's an implementation detail.
Update to airbase 29

This makes the dependency plugin compatible with Java 8
Remove unused methods
Remove getter functions from ByteCodeExpression
Remove getter functions from JmxColumnHandle
Remove getter functions from JmxRecordSetProvider
Remove getter functions from QueryInfo
Remove getter functions from SqlStageExecution
Remove getter functions from SqlTask
Remove getter functions from StageInfo
Remove getter functions from TaskInfo
Remove getter/predicate functions from HeartbeatFailureDetector
Remove getter functions from ColumnHandle
Remove getter functions from FunctionInfo