Added initial implementation of http://www.reddit.com/r/dailyprogrammer/comments/pkwb1/2112012_challenge_3_intermediate/
Added some unit tests.
Refactored the encrypt and decrypt operations so that the cypherbet is calculated within the class and the alphabet is a class constant so doesn't need to be defined or passed in the program.
Updated README.md.
Merge pull request #6 from TimCollins/3-Int-Cipher

3 int cipher