--- split([sep[, limit]])

    ʸ sep ǻꤵ줿ѥˤäʬ䤷˳Ǽ
    ޤsep  1 ХȤʸʤ餽ʸڤȤʬ
    䤷ޤ2 ХȰʾʸʤɽ˥ѥ뤵ޤ
    sep  nil Ǥ뤫άˤѿ
    $; ͤڤʸȤƻѤޤ

    sep  1 Ĥζ(' ')λޤ $; Ѥ
    Ǥͤ nil λˤƬζƶʬ
    ޤ

      p "   a \t  b \n  c".split(/\s+/) # => ["", "a", "b", "c"]
      p "   a \t  b \n  c".split        # => ["a", "b", "c"] ($;ΥǥեͤnilǤ)
      p "   a \t  b \n  c".split(' ')   # => ["a", "b", "c"]

    limit ά줿(ޤ 0 λ)ˤζʸ
    ޤ
    limit ꤵơͤǤʤˤϺ limit 
    ĤΥեɤʬ䤷ޤ
    limit ͤλˤ̵¤礭 limit ꤵ줿
    Τ褦ʬ䤷ޤ

      # limit άϡ0 ꤷΤƱζʸϼ
      p "a,b,c,,,".split(/,/)      # => ["a", "b", "c"]
      p "a,b,c,,,".split(/,/, 0)   # => ["a", "b", "c"]

      # limit  ΥեɿʤϺǸǤ˻Ĥꤹ٤Ƥ
      p "a,b,c,,,".split(/,/, 3)   # => ["a", "b", "c,,,"]

      # limit  -1 ΥեɿʾξϺΥեɿꤷΤƱ
      p "a,b,c,,,".split(/,/, 6)     # => ["a", "b", "c", "", "", ""]
      p "a,b,c,,,".split(/,/, -1)    # => ["a", "b", "c", "", "", ""]
      p "a,b,c,,,".split(/,/, 100)   # => ["a", "b", "c", "", "", ""]

    sep ǻꤵ줿ѥ󤬶ʸȥޥåʸ 
    1 ʸĤʬ䤵ޤ($KCODE Ŭڤꤵ
    дǧʸñ̤ʬ䤷ޤ)㤨:

      p 'hi there'.split(/ */).join(':')
      # => "h:i:t:h:e:r:e"

    sep ǻꤵ줿ѥ˳̤ޤޤƤˤϡƳ
    Υѥ˥ޥåʸ˴ޤޤޤ̤ʣ
    ϡޥåΤ˴ޤޤޤ㤨:

      p '1-10,20'.split(/([-,])/)   # => ["1", "-", "10", ",", "20"]
      p '1-10,20'.split(/(-)|(,)/)  # => ["1", "-", "10", ",", "20"]

    ruby 1.7 feature: 1.6 ϡsep  2 ʸʾʸ
    ξ硢ʸɽ˥ѥ뤷Ƥޤ1.7 ʹߤϡ
    ʸ󤽤ΤΤѥˤʤޤ

