code: func OpenFile(filename string) (apk *Apk, err error) {
  	f, err := os.Open(filename)
  	if err != nil {
  		return nil, err
  	}
  	defer func() {
  		if err != nil {
  			f.Close()
  		}
  	}()
  	fi, err := f.Stat()
  	if err != nil {
  		return nil, err
  	}
  	apk, err = OpenZipReader(f, fi.Size())
  	if err != nil {
  		return nil, err
  	}
  	apk.f = f
  	return
  }
docs: // OpenFile will open the file specified by filename and return Apk