adding blocking and non-blocking rtsp stream

This might fix the stream errors in issue #25
Also refactored the code a bit since we do not want to display a window from within the API (offload to the person implementing it).

util.py

@@ -0,0 +1,11 @@
+from threading import Thread
+
+
+def threaded(fn):
+    def wrapper(*args, **kwargs):
+        thread = Thread(target=fn, args=args, kwargs=kwargs)
+        thread.daemon = True
+        thread.start()
+        return thread
+
+    return wrapper