Execution example::

  tokenize TokenBigram "Groonga is a fast fulltext earch engine!"
  # [
  #   [
  #     0,
  #     1337566253.89858,
  #     0.000355720520019531
  #   ],
  #   [
  #     {
  #       "value": "Gr",
  #       "position": 0,
  #       "force_prefix": false,
  #       "force_prefix_search": false
  #     },
  #     {
  #       "value": "ro",
  #       "position": 1,
  #       "force_prefix": false,
  #       "force_prefix_search": false
  #     },
  #     {
  #       "value": "oo",
  #       "position": 2,
  #       "force_prefix": false,
  #       "force_prefix_search": false
  #     },
  #     {
  #       "value": "on",
  #       "position": 3,
  #       "force_prefix": false,
  #       "force_prefix_search": false
  #     },
  #     {
  #       "value": "ng",
  #       "position": 4,
  #       "force_prefix": false,
  #       "force_prefix_search": false
  #     },
  #     {
  #       "value": "ga",
  #       "position": 5,
  #       "force_prefix": false,
  #       "force_prefix_search": false
  #     },
  #     {
  #       "value": "a ",
  #       "position": 6,
  #       "force_prefix": false,
  #       "force_prefix_search": false
  #     },
  #     {
  #       "value": " i",
  #       "position": 7,
  #       "force_prefix": false,
  #       "force_prefix_search": false
  #     },
  #     {
  #       "value": "is",
  #       "position": 8,
  #       "force_prefix": false,
  #       "force_prefix_search": false
  #     },
  #     {
  #       "value": "s ",
  #       "position": 9,
  #       "force_prefix": false,
  #       "force_prefix_search": false
  #     },
  #     {
  #       "value": " a",
  #       "position": 10,
  #       "force_prefix": false,
  #       "force_prefix_search": false
  #     },
  #     {
  #       "value": "a ",
  #       "position": 11,
  #       "force_prefix": false,
  #       "force_prefix_search": false
  #     },
  #     {
  #       "value": " f",
  #       "position": 12,
  #       "force_prefix": false,
  #       "force_prefix_search": false
  #     },
  #     {
  #       "value": "fa",
  #       "position": 13,
  #       "force_prefix": false,
  #       "force_prefix_search": false
  #     },
  #     {
  #       "value": "as",
  #       "position": 14,
  #       "force_prefix": false,
  #       "force_prefix_search": false
  #     },
  #     {
  #       "value": "st",
  #       "position": 15,
  #       "force_prefix": false,
  #       "force_prefix_search": false
  #     },
  #     {
  #       "value": "t ",
  #       "position": 16,
  #       "force_prefix": false,
  #       "force_prefix_search": false
  #     },
  #     {
  #       "value": " f",
  #       "position": 17,
  #       "force_prefix": false,
  #       "force_prefix_search": false
  #     },
  #     {
  #       "value": "fu",
  #       "position": 18,
  #       "force_prefix": false,
  #       "force_prefix_search": false
  #     },
  #     {
  #       "value": "ul",
  #       "position": 19,
  #       "force_prefix": false,
  #       "force_prefix_search": false
  #     },
  #     {
  #       "value": "ll",
  #       "position": 20,
  #       "force_prefix": false,
  #       "force_prefix_search": false
  #     },
  #     {
  #       "value": "lt",
  #       "position": 21,
  #       "force_prefix": false,
  #       "force_prefix_search": false
  #     },
  #     {
  #       "value": "te",
  #       "position": 22,
  #       "force_prefix": false,
  #       "force_prefix_search": false
  #     },
  #     {
  #       "value": "ex",
  #       "position": 23,
  #       "force_prefix": false,
  #       "force_prefix_search": false
  #     },
  #     {
  #       "value": "xt",
  #       "position": 24,
  #       "force_prefix": false,
  #       "force_prefix_search": false
  #     },
  #     {
  #       "value": "t ",
  #       "position": 25,
  #       "force_prefix": false,
  #       "force_prefix_search": false
  #     },
  #     {
  #       "value": " e",
  #       "position": 26,
  #       "force_prefix": false,
  #       "force_prefix_search": false
  #     },
  #     {
  #       "value": "ea",
  #       "position": 27,
  #       "force_prefix": false,
  #       "force_prefix_search": false
  #     },
  #     {
  #       "value": "ar",
  #       "position": 28,
  #       "force_prefix": false,
  #       "force_prefix_search": false
  #     },
  #     {
  #       "value": "rc",
  #       "position": 29,
  #       "force_prefix": false,
  #       "force_prefix_search": false
  #     },
  #     {
  #       "value": "ch",
  #       "position": 30,
  #       "force_prefix": false,
  #       "force_prefix_search": false
  #     },
  #     {
  #       "value": "h ",
  #       "position": 31,
  #       "force_prefix": false,
  #       "force_prefix_search": false
  #     },
  #     {
  #       "value": " e",
  #       "position": 32,
  #       "force_prefix": false,
  #       "force_prefix_search": false
  #     },
  #     {
  #       "value": "en",
  #       "position": 33,
  #       "force_prefix": false,
  #       "force_prefix_search": false
  #     },
  #     {
  #       "value": "ng",
  #       "position": 34,
  #       "force_prefix": false,
  #       "force_prefix_search": false
  #     },
  #     {
  #       "value": "gi",
  #       "position": 35,
  #       "force_prefix": false,
  #       "force_prefix_search": false
  #     },
  #     {
  #       "value": "in",
  #       "position": 36,
  #       "force_prefix": false,
  #       "force_prefix_search": false
  #     },
  #     {
  #       "value": "ne",
  #       "position": 37,
  #       "force_prefix": false,
  #       "force_prefix_search": false
  #     },
  #     {
  #       "value": "e!",
  #       "position": 38,
  #       "force_prefix": false,
  #       "force_prefix_search": false
  #     },
  #     {
  #       "value": "!",
  #       "position": 39,
  #       "force_prefix": false,
  #       "force_prefix_search": false
  #     }
  #   ]
  # ]
