Add practice exercise: rotational-cipher

[jimmytty]

• difficulty set to 8.
• simple implementation.

[jimmytty]

🤔 Looking at old code, I think I still did the code indentation wrong... I'll wait for your evaluation.
For example, I indented code like this:

UPDATE ...
    SET ...

and, in old code, there's no indentation at this level...

[IsaacG]

🤔 Looking at old code, I think I still did the code indentation wrong... I'll wait for your evaluation. For example, I indented code like this:

Yeah. I noticed but I assumed it was consistent with existing files so didn't bother saying anything. I think most of the prior files were at least fairly consistent within each file.

I'm waiting for @vaeng to make the auto indenter a thing. #16