Merge pull request #54 from matthayes/master

Make DistinctBy implement Accumulator interface
combine behaviors of BagConcat and BagUnion
add back in licensing information
fix udf name in documenation
Merge pull request #56 from william-g-vaughan/master

Union the functionality of BagUnion and BagConcat
random functions are non-deterministic
Merge pull request #57 from njwhite/randint

random functions are non-deterministic
Add Nondeterministic annotation where appropriate