Merge v4 changes: metadata instead of classname, rel transformations

This was merged a little prematurely and, more importantly, didn't give us a clear record of where it happened.

This commits the changes described in https://github.com/neo4jrb/neo4j/pull/595. You can read about the changes at [https://github.com/neo4jrb/neo4j/wiki/Neo4j.rb-v4-Introduction](https://github.com/neo4jrb/neo4j/wiki/Neo4j.rb-v4-Introduction) and discuss them at [https://github.com/neo4jrb/neo4j/issues/596](https://github.com/neo4jrb/neo4j/issues/596).