proto/packet: Fix R/W fields for LoginInfo.

- Entity field wasn't being Read or Writen from io.Reader or to
io.Writer.
proto/ping: Little refactor for ping.Prepare.
Add pkg: server/player.
Add pkg: server. First *WORKING* server impl.
Add pkg: util/crypto/cfb8.

- Required by pkg "server".
Add pkg: util/iodebug.