// source: https://cryptopals.com/sets/1/challenges/3
/*
Single-byte XOR cipher
The hex encoded string:
1b37373331363f78151b7f2b783431333d78397828372d363c78373e783a393b3736
... has been XOR'd against a single character. Find the key, decrypt the message.
You can do this by hand. But don't: write code to do it for you.
How? Devise some method for "scoring" a piece of English plaintext. Character frequency is a good metric. Evaluate each output and choose the one with the best score.
*/