Add --echo option to cli

pytchat/cli/echo.py

@@ -0,0 +1,17 @@
+import pytchat
+from ..util.extract_video_id import extract_video_id
+
+
+class Echo:
+    def __init__(self, video_id):
+        self.video_id = extract_video_id(video_id)
+    
+    def run(self):
+        livechat = pytchat.create(self.video_id)
+        while livechat.is_alive():
+            chatdata = livechat.get()
+            for c in chatdata.sync_items():
+                print(f"{c.datetime} [{c.author.name}] {c.message} {c.amountString}")
+
+
+