Add first to Message class (#340)

* Add `first` to Message class

Boolean representing whether it's a first message or not. Could be None.

* Update changelog.rst

* Update twitchio/message.py

Co-authored-by: Tom <[email protected]>

* Update twitchio/message.py

Co-authored-by: Tom <[email protected]>

* Update twitchio/message.py

Co-authored-by: Tom <[email protected]>

* Update twitchio/message.py

Co-authored-by: Tom <[email protected]>

* Update message.py

* Update message.py

Co-authored-by: Tom <[email protected]>

Author: preeded

docs/changelog.rst

@@ -5,6 +5,7 @@ Master
 ======
 - TwitchIO
     - Additions
+        - Added :attr:`~twitchio.Message.first` to :class:`~twitchio.Message`
         - Added :func:`~twitchio.PartialUser.fetch_channel_emotes` to :class:`~twitchio.PartialUser`
         - Added :func:`~twitchio.Client.fetch_global_emotes` to :class:`~twitchio.Client`
         - Added :func:`~twitchio.Client.event_channel_join_failure` event:

twitchio/message.py

@@ -39,6 +39,8 @@ class Message:
         The content of this message.
     echo: :class:`bool`
         Boolean representing if this is a self-message or not.
+    first: :class:`bool`
+        Boolean representing whether it's a first message or not.
 
     """
 
@@ -47,6 +49,7 @@ class Message:
         "content",
         "_author",
         "echo",
+        "first",
         "_timestamp",
         "_channel",
         "_tags",
@@ -61,6 +64,12 @@ def __init__(self, **kwargs):
         self._tags = kwargs.get("tags")
         self.echo = kwargs.get("echo", False)
 
+        self.first = False
+        if self._tags is not None:
+            first = self._tags.get("first-msg")
+            if first == "1":
+                self.first = True
+
         try:
             self._id = self._tags["id"]
             self._timestamp = self._tags["tmi-sent-ts"]