--- readlines([rs])

    ǡɤ߹ǡγƹԤǤȤƤ֤ޤ
    IO  EOF ãƤж [] ֤ޤ

    Ԥζڤϰ rs ǻꤷʸˤʤޤrs 
    ǥեͤϥƥѿ $/ ͤǤ

    rs  nil ꤹȹԶڤʤȤߤʤޤ
    ʸ "" ꤹϢ³ԤԤζڤȤߤʤޤ
    (ѥ饰ե⡼)

