On main():

- Remove blank likes
- Update the order of the arguments to DirectoryTree constructor

On parse_cmd_line_arguments():

- Remove unneeded upper case letter from strings
- Move the version attribute up
- Remove the unneeded type argument because str is the default type for command-line arguments

- Add a missing import
- Add a new module-level constant to provide a new prefix

On DirectoryTree

- Swap the order of the argument in the class initializer
- Update functions calls and rename item to entry

On _TreeGenerator

- Rename the first argument of the initializer to be more consistent with the current API
- Turn .dir_only into a non-public attribute
- Use a deque instead of a list to optimize the insertions of item at the beginning of the data structure
- Rename the dir argument to directory so we can avoid name collisions with the built-in dir() function
- Remove the path local variable joining
- Rename path to entry so we maintain a uniform naming
- Move the path argument to the beginning of the argument in _add_file(). Also, it was renamed from path to file