Add SortMergeJoinExample to tez-examples

In the current join example, the inputs of JoinProcessor is unordered so that it will always need to load one input into memory, and stream another input. This only fit for the case when one dataset is small enough to fit into memory ( even use no-broadcast, memory may not be enough ). So I'd like to add another join example that make the inputs of JoinProcessor is ordered. ( using OrderedPartitionedKVEdgeConfig ). This kind of join could been used when both of the 2 datasets are large.