add Node.__iter__
examples: add schema.py

Usage:

    PYTHONPATH=. python examples/schema.py controller.applications.bcf.tenant.segment

Outputs:

    controller/applications/bcf/tenant/segment (list)
      endpoint (list)
        attachment-point
          interface : string
          switch : string
          vlan : integer
          port-group : string
        description : string
        origination : string
        mac : string
        ip-address (list)
          ip-address : union
        name : string
      name : string
      member-vlan : integer
      port-group-membership-rule (list)
        origination : string
        vlan : integer
        description : string
        port-group : string
      origination : string
      switch-port-membership-rule (list)
        interface : string
        switch : string
        vlan : integer
        origination : string
        description : string
      internal-vlan : integer
      description : string