--- sort
--- sort {|a, b| ... }

    ƤǤ򾺽˥Ȥ֤ޤ

    ֥åʤΤȤ <=> ᥽åɤǤФƸƤӡη
    ̤Ȥ˥Ȥޤ

    <=> ʳǥȤϡ֥åꤷޤξ
    ֥åɾ̤򸵤˥Ȥޤ֥åͤϡa>b 
    Ȥa==b ΤȤ 0a<b ΤȤ򡢴Ԥ
    ޤ֥åʳ֤Ȥ㳰 TypeError ȯ
    ޤ

    Enumerable#sort ϰǤϤޤ (unstable sort)

     ӷ̤ƱǤϸν̤¤֥Ȥ
    ְʥ (stable sort)פȸޤ

