Added option to get stats returned when running a cypher query.

I recently had to run `CREATE UNIQUE` for relationships and the only way to find out if a relation was created is to get hold of te stats and look at `stats.relationships_created` like this:

    db.cypherQuery(q, {}, function(err, res) {
        if(res.stats.relationships_created > 0) {
            //Relation created
        }
    })

I wasn't sure where you wanted this setting to be set, but since it's not very common I figured that it's easiest just to add it as a parameter to the function call.