# Rotational Cipher

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
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  `omg` gives `trl`
- ROT0  `c` gives `c`
- ROT26 `Cool` gives `Cool`
- ROT13 `The quick brown fox jumps over the lazy dog.` gives `Gur dhvpx oebja sbk whzcf bire gur ynml qbt.`
- ROT13 `Gur dhvpx oebja sbk whzcf bire gur ynml qbt.` gives `The quick brown fox jumps over the lazy dog.`

This is a good exercise to experiment with non-standard string literals and metaprogramming.

A short introduction to non-standard string literals can be found in this [blog post](http://iaindunning.com/blog/julia-unicode.html). A detailed metaprogramming guide can be found in the [manual](http://docs.julialang.org/en/stable/manual/metaprogramming/).

You can extend your solution by adding the functionality described below. To test your solution, you have to remove the comments at the end of `runtests.jl` before running the tests as usual.

Bonus A only requires basics as outlined in the blog post. Bonus B requires significantly more knowledge of metaprogramming in Julia.

## Bonus A
Implement a string literal that acts as `ROT13` on the string:
```julia
R13"abcdefghijklmnopqrstuvwxyz" == "nopqrstuvwxyzabcdefghijklm"
```

## Bonus B
Implement string literals `R<i>`, `i = 0, ..., 26`, that shift the string for `i` values:
```julia
R0"Hello, World!" == "Hello, World!"
R4"Testing 1 2 3 testing" == "Xiwxmrk 1 2 3 xiwxmrk"
R13"abcdefghijklmnopqrstuvwxyz" == "nopqrstuvwxyzabcdefghijklm"
```

## Source

Wikipedia [https://en.wikipedia.org/wiki/Caesar_cipher](https://en.wikipedia.org/wiki/Caesar_cipher)


## Submitting Incomplete Solutions
It's possible to submit an incomplete solution so you can see how others have completed the exercise.