def find(&block)
      found = []
      self.each_file do |name, data|
        ret = block.call(name, data)
        found << name if ret
      end
      found
    end
def find(&block)
      found = []
      self.each_file do |name, data|
        ret = block.call(name, data)
        found << name if ret
      end
      found
    end
find files which is matched with block condition
 @yield [name, data] find condition
 @yieldparam [String] name file name in apk
 @yieldparam [String] data file data in apk
 @yieldreturn [Array] Array of matched entry name
 @return [Array] Array of matched entry name
 @example
   apk = Apk.new(path)
   elf_files = apk.find  { |name, data|  data[0..3] == [0x7f, 0x45, 0x4c, 0x46] } # ELF magic number