[New Exercise] Add affine cipher exercise

[Sencudra]

No description provided.

[github-actions]

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[github-actions]

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[Sencudra]

@meatball133 fyi, please reopen and review, when possible

[meatball133]

These changes should likely go into another pr, just saying this for future cases.

[Sencudra]

Yeah, no problem, I can do it now. Here we are:

#892

[meatball133]

I notice some of the files have an extra line in the beging of the file, feels like that shouldn't be there

[Sencudra]

No specific reason, it's just my old habbit, removed.