Execution example::

  load --table Replies2
  [
  {"_key": 1, "content": "I'm using Rroonga too!"},
  {"_key": 2, "content": "I'm using Groonga and Mroonga and Rroonga!"},
  {"_key": 3, "content": "I'm using Nroonga too!"}
  ]
  # [[0, 1337566253.89858, 0.000355720520019531], 3]
  load --table Comments2
  [
  {"_key": 1, "content": "I'm using Groonga too!", "comment": 1},
  {"_key": 2, "content": "I'm using Groonga and Mroonga!", "comment": 2},
  {"_key": 3, "content": "I'm using Mroonga too!"}
  ]
  # [[0, 1337566253.89858, 0.000355720520019531], 3]
  load --table Articles2
  [
  {"content": "Groonga is fast!", "comment": 1},
  {"content": "Groonga is useful!", "comment": 2},
  {"content": "Mroonga is fast!", "comment": 3}
  ]
  # [[0, 1337566253.89858, 0.000355720520019531], 3]
