Implement Directory Operations: mkdir, rmdir, readdir

Implement directory operations.

Requirements:

• Create directories with mkdir()
• Remove empty directories with rmdir()
• Read directory contents with opendir()/readdir()
• List all entries in directory
• Handle . and .. special entries
• Check return values for errors
• Print error messages with perror()
• Demonstrate creating nested directories

Test:

• Create directories
• List directory contents
• Remove directories
• Handle errors properly