Add getter for Message-ID

lib/nntp/tiny/message.py

@@ -65,6 +65,11 @@ class Message():
     def header(self, key: str):
         return self.headers.get(key.lower())
 
+    def id(self) -> str:
+        match = self.RE_MESSAGE_ID.match(self.header('Message-ID'))
+
+        return match[1]
+
     def date(self):
         try:
             return search_dates(self.headers['date'])[0][1]