Added file and files keyword arguments

Added file and files keyword arguments into the edit function
Edited docstrings for the file and files keyword arguments

Author: caffe-ian

discord/message.py

@@ -1183,6 +1183,8 @@ async def edit(
         content: Optional[str] = MISSING,
         embed: Optional[Embed] = MISSING,
         embeds: List[Embed] = MISSING,
+        file: Sequence[File] = MISSING,
+        files: List[Sequence[File]] = MISSING,
         attachments: List[Attachment] = MISSING,
         suppress: bool = MISSING,
         delete_after: Optional[float] = None,
@@ -1211,6 +1213,10 @@ async def edit(
             To remove all embeds ``[]`` should be passed.
 
             .. versionadded:: 2.0
+        file: Sequence[:class:`File`]
+            A new file to add to the message.
+        files: List[Sequence[:class:`File`]]
+            New files to add to the message.
         attachments: List[:class:`Attachment`]
             A list of attachments to keep in the message. If ``[]`` is passed
             then all attachments are removed.
@@ -1244,7 +1250,8 @@ async def edit(
             Tried to suppress a message without permissions or
             edited a message's content or embed that isn't yours.
         ~discord.InvalidArgument
-            You specified both ``embed`` and ``embeds``
+            You specified both ``embed`` and ``embeds`` or
+            specified both ``file`` and ``files``.
         """
 
         payload: Dict[str, Any] = {}
@@ -1289,8 +1296,54 @@ async def edit(
                 payload['components'] = view.to_components()
             else:
                 payload['components'] = []
+                
+        if file is not None and files is not None:
+            raise InvalidArgument('cannot pass both file and files parameter to send()')
 
-        data = await self._state.http.edit_message(self.channel.id, self.id, **payload)
+        if file is not None:
+            if not isinstance(file, File):
+                raise InvalidArgument('file parameter must be File')
+
+            try:
+                data = await state.http.edit_files(
+                    channel.id,
+                    self.id,
+                    files=[file],
+                    attachments=attachments,
+                    suppress=suppress,
+                    allowed_mentions=allowed_mentions,
+                    content=content,
+                    embed=embed,
+                    embeds=embeds,
+                    components=components,
+                )
+            finally:
+                file.close()
+
+        elif files is not None:
+            if len(files) > 10:
+                raise InvalidArgument('files parameter must be a list of up to 10 elements')
+            elif not all(isinstance(file, File) for file in files):
+                raise InvalidArgument('files parameter must be a list of File')
+
+            try:
+                data = await state.http.edit_files(
+                    channel.id,
+                    self.id,
+                    files=files,
+                    attachments=attachments,
+                    suppress=suppress,
+                    content=content,
+                    embed=embed,
+                    embeds=embeds,
+                    allowed_mentions=allowed_mentions,
+                    components=components,
+                )
+            finally:
+                for f in files:
+                    f.close()
+        else:
+            data = await self._state.http.edit_message(self.channel.id, self.id, **payload)
         message = Message(state=self._state, channel=self.channel, data=data)
 
         if view and not view.is_finished():