A folding cipher where the mappings are done by "folding the alphabet." This way, "a" maps to "z", "b" maps to "y", "c" maps to "x", and so on.
https://en.wikipedia.org/wiki/Atbash
Plain: abcdefghijklmnopqrstuvwxyz
Cipher: zyxwvutsrqponmlkjihgfedcba
For the class Cipher, implement a class method encode that takes a word as an argument returns the encoded word
Example usage:
Cipher.encode("hello")
=> "svool"
Cipher.encode("peter")
=> "kvgvi"
For the class Cipher, implement a class method decode that takes a word as an argument returns the decoded word