Add HashJoin
Add shuffle, shuffleReduce function to Silk
Represent GroupBy and Sort operation with shuffle and shuffleReduce
Suppress log4j warning in test
Enforce RangePartitioner in Sort operation
Introduce ShuffleMerge operation to implement distributed hash-join algorithm
Switch the algorithm according to the input Silk byte size
Recursive hash-join
Fix block size check
Add TakeHead optimizer
Removed xerial.silk.cluster package. All silk framework components are moved to xerial.silk.framework package
Fixes test case compilation. Removed 'Not a simple type' warning in sbt by exposing API as a global trait