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.

irc_struct.go

@@ -33,7 +33,7 @@ type Connection struct {
 	nickcurrent string //The nickname we currently have.
 	user        string
 	registered  bool
-	events      map[string]map[string]func(*Event)
+	events      map[string]map[int]func(*Event)
 
 	QuitMessage string
 	lastMessage time.Time