Execution example::

  load --table Comment
  [
  {"_key": 1, "name": "A", "content": "groonga"},
  {"_key": 2, "name": "B", "content": "groonga"},
  {"_key": 3, "name": "C", "content": "rroonga"},
  {"_key": 4, "name": "A", "content": "mroonga"},
  ]
  # [[0,1337566253.89858,0.000355720520019531],4]
  load --table Blog
  [
  {"_key": "groonga's blog", "content": "content of groonga's blog", comments: [1, 2, 3]},
  {"_key": "mroonga's blog", "content": "content of mroonga's blog", comments: [2, 3, 4]},
  {"_key": "rroonga's blog", "content": "content of rroonga's blog", comments: [3]},
  ]
  # [[0,1337566253.89858,0.000355720520019531],3]
