Create PeerInterface.class

PeerInterface
 * TODO : make a method recieveUnknownMessage that identifies a message and runs the relevant function (ie recieveHandshake, recievePiece)
 * make method recieveHandshake() to recieve handshakes from a potential peer
 * make a method that runs a different message method based on input
 * make methods for recieving and sending bittorrent protocol messages that haven't been coded yet
 * create a test client to check compatibility with this class

Note - RUBTClient has not been modified to work with this yet
Suggestion - a utility class to hold methods like byteArrayToInt() and intToByteArray()