Added Cipher class

Cipher can encode and decode strings, using a keyword set by the user.
Something is wrong with the index of search for chars -> string arrays.
Improvement of Cipher -- Works!

Basically, I forgot that chars needed to be converted to lowercase or
uppercase, to be made consistent. I also created a dictionary that is
created with both the normal alphabet, and the altered one, for easy
mappings between both structures.
Merge pull request #2 from InspiredIdealist/master

Fix of Cipher class -- Now actually encodes and decodes strings! yippee!