You are asked to write a simple cypher that rotates every character (in range [a-zA-Z], special chars will be ignored by the cypher) by 13 chars. As an addition to the original ROT13 cypher, this cypher will also cypher numerical digits ([0-9]) with 5 chars.
Example:
"The quick brown fox jumps over the 2 lazy dogs"
will be cyphered to:
"Gur dhvpx oebja sbk whzcf bire gur 7 ynml qbtf"
Your task is to write a ROT13.5 (ROT135) method that accepts a string and encrypts it. Decrypting is performed by using the same method, but by passing the encrypted string again.
Note: when an empty string is passed, the result is also empty.