Vigenère cypher function (https://en.wikipedia.org/wiki/Vigenère_cipher)
Returns the encoding of aStr after applying the Vigenère cypher with the key aKey. aStr is supposed to be a string composed uniquely from a-z characters, and aKey is a string composed uniquely from a-z characters.
aStr
aKey
a-z
the string to cypher
the key to use for the Vigenère cypher
the cyphered string
Vigenère cypher function (https://en.wikipedia.org/wiki/Vigenère_cipher)
Returns the encoding of
aStrafter applying the Vigenère cypher with the keyaKey.aStris supposed to be a string composed uniquely froma-zcharacters, andaKeyis a string composed uniquely froma-zcharacters.