Added support for 2i queries and MR emulated multigets

Moved riak-erlang-client dependency from version 1.2.1 to 1.3.3.

Added ability to add secondary indexes and benchmark simple secondary index queries. 

Also added functionality to benchmark basic multi-get queries emulated over map/reduce. Although we discourage implementing multi-gets on top of map/reduce, having the functionality there will allow users contemplating using it to more easily set up benchmarks and examine what level of performance one can typically expect and what effects it may have on the cluster.