Send and receive messages

Also correctly respond to PING with the id, escape some XML content, but not
always

src/irc/iid.hpp

@@ -20,6 +20,7 @@ class Iid
 {
 public:
   explicit Iid(const std::string& iid);
+  explicit Iid();
 
   std::string chan;
   std::string server;