added 2d matrix example (chapter 11)
added flat matrix example (chapter 11)
wrote linked list example (chapter 11)
added queues example (chapter 11)
wrote queues.lua (chapter 11)
updated queues.lua (chapter 11)
added sets example (chapter 11)
added string buffer example (chapter 11)
wrote word frequency with ignore list (chapter 11)
added self-describing data format example (chapter 11)
wrote serialize.lua (chapter 12)
added sets example (chapter 13)
added sets solution (chapter 13)