* Added two new challenges. The first related to advanced file display, the second to navigating nested directories.

* Added hidden directory and corrected symlink

* Finalised pull request

* Removed hidden directory (from challenges and challenges.yaml) as difficult to sync via git

* Added file to hidden directory so I can commit it

* Made description of list_files_adv more specific

* Updated nested_dirs description as requested

* In cases where running commands was timing out due to server issues
commands with tests would fall through and pass. Now we will throw.

* Use a random script name so you don't see it when commands fail.

…ent'