Fixed issue with canonical edge partitioner.
Added PartitionStrategy option
Updated documentation
Fixed code review changes.
Added partitioner to GraphImpl constructor args.
Added accessVertexAttr func which somehow got lost in a merge.
Merge branch 'master' into partitioners
Addressed code review comments.
Re-added slaves file for compatibility with Spark
Merge pull request #62 from dcrankshaw/partitioners

Allow user to choose a partitioner at runtime