Rotational Cipher
Welcome to Rotational Cipher on Exercism's Elixir Track.
If you need help running the tests or submitting your code, check out HELP.md.
Instructions
Create an implementation of the rotational cipher, also sometimes called the Caesar cipher.
The Caesar cipher is a simple shift cipher that relies on transposing all the letters in the alphabet using an integer key between 0 and 26.
Using a key of 0 or 26 will always yield the same output due to modular arithmetic.
The letter is shifted for as many values as the value of the key.
The general notation for rotational ciphers is ROT + <key>.
The most commonly used rotational cipher is ROT13.
A ROT13 on the Latin alphabet would be as follows:
Plain:  abcdefghijklmnopqrstuvwxyz
Cipher: nopqrstuvwxyzabcdefghijklm
It is stronger than the Atbash cipher because it has 27 possible keys, and 25 usable keys.
Ciphertext is written out in the same formatting as the input including spaces and punctuation.
Examples
- ROT5 
omggivestrl - ROT0 
cgivesc - ROT26 
CoolgivesCool - ROT13 
The quick brown fox jumps over the lazy dog.givesGur dhvpx oebja sbk whzcf bire gur ynml qbt. - ROT13 
Gur dhvpx oebja sbk whzcf bire gur ynml qbt.givesThe quick brown fox jumps over the lazy dog. 
Source
Created by
- @DoggettCK
 
Contributed to by
- @angelikatyborska
 - @Cohen-Carlisle
 - @devonestes
 - @neenjaw
 - @sotojuan
 
Based on
Wikipedia - https://en.wikipedia.org/wiki/Caesar_cipher