: scan( pattern: Regexp )  ->  String
    ݥ󥿤 pattern ʸΥޥåޤ
    ޥå顢ݥ󥿤ʤɽ˥ޥå
    ʬʸ֤ޤޥåʤä nil ֤ޤ

        s = StringScanner.new('test string')
        p s.scan(/\w+/)   #=> "test"
        p s.scan(/\w+/)   #=> nil
        p s.scan(/\s+/)   #=> " "
        p s.scan(/\w+/)   #=> "string"
        p s.scan(/./)     #=> nil

