(If you are less comfortable with this assignment) Write a Python program that implements the Caesar cipher, allowing the user to specify the plaintext and the shift (for encryption), or the ciphertext and the shift (for decryption). You can have a single program that encrypts and decrypts, or you can separate these functions into two programs. Make sure you handle both upper case and lower case letters, but numbers and other characters (like spaces) should be passed through unmodified.