Manipulating Directories
------------------------
- Command: make-directory directory-name
Create a new directory called DIRECTORY-NAME.
- Command: delete-directory directory-name
Delete the directory called DIRECTORY-NAME. This only succeeds if
the directory in question is empty, otherwise an error is
signalled.
- Function: directory-files directory-name
Returns a list of the names of all items in the directory whose
name is DIRECTORY-NAME. The names in the list will be relative to
the directory DIRECTORY-NAME.
(directory-files "/tmp/foo"
=> ("bar" "subdir" "xyz" "." "..")