rfw.go
func Open(path string, mode os.FileMode) (*Writer, error) {
	var w Writer
	w.path = path
	w.mode = mode
	err := w.open()
	return &w, err
}
func Open(path string, mode os.FileMode) (*Writer, error) {
	var w Writer
	w.path = path
	w.mode = mode
	err := w.open()
	return &w, err
}
/*
Open returns a new Writer at the specified path.

If the file does not exist it will be created with the specified mode.
If the file does exist it will be appended to.
*/