Release 3.0.0.alpha.15 (the relationships edition)

 - create CypherQuery class; intent to rearchitect QueryBuilder for a persistent query obj that can be passed; support stringing several types, e.g. (n0)-[r0]->(n1)<-[r1]-(n2)
 - use new CypherQuery in Server::CypherNode/Relationship#match; Server::Session#load_node
 - add Server::Session#create_rel, #load_relationship, #find_all_rels, #find_rels, and #search_result_to_enumerable_rels
 - add option to restrict node searches by label
 - add several querying methods to Server::CypherRelationship
 - uptick alpha version