One of the types of arguments that I find myself most often passing to `argparse.ArgumentParser` is paths. I think that I am probably not alone in frequent usage of paths as arguments. Given this, it would be extremely helpful to have an `argparse.Action` in `argparse` or an type similar to `FileType` that converted the string to a path. A path type factory could also have an arguments to optionally check if the path exists, or is a directory, or other similar predicates.