Implement the ciphers outlined in the README

[arosspope]

[glarsen]

@arosspope I have a working implementation of the PlayFair cipher to contribute. I still have some documentation and refactoring to complete. Would you like me to send the PR as soon as things are ready or wait until #35 is merged in?

[arosspope]

Create your PR but you may have to merge in master during this process (and change some versioning information) if #35 gets merged before yours.

[teskje]

I'd like to take the Porta cipher, if I may.

[arosspope]

Please, by all means. Could you please create an issue and assign it to yourself? Just so it's clear that you have taken that cipher