Recursive Directory Listing
Created by: Assaad Youssef Abou-Rached
Scan directory and list its content (folders, subfolders, and files)
Built-in functions to be used: is_dir(), opendir(), readdir(), closedir()
Built-in constants to be used: DIRECTORY_SEPARATOR
We will build a simple function that scans a given directory and loop through its content recuresivly, saving its content
to an array and return the array.