BREAKING CHANGES: Run callbacks in main thread and int callback id.

Execute callbacks in main thread. This will break callbacks that
use a long time to execute. Create your own thread in AddCallback
using gorutines on long running callbacks.

Use deterministic IDs for AddCallback. Changes the id from SHA-hash
to int.

README.markdown

@@ -46,6 +46,20 @@ AddCallback Example
 		//event.Arguments[0] Contains the channel
 	});
 
+Please note: Callbacks are run in the main thread. If a callback needs a long
+time to execute please run it in a new thread.
+
+Example:
+
+        ircobj.AddCallback("PRIVMSG", func(event *irc.Event) {
+		go func(event *irc.Event) {
+                        //event.Message() contains the message
+                        //event.Nick Contains the sender
+                        //event.Arguments[0] Contains the channel
+		}(e)
+        });
+
+
 Commands
 --------
 	ircobj := irc.IRC("<nick>", "<user>") //Create new ircobj