Add the new poll attribute to Message types

Adds the new poll key to the Message structures we have, as well as
mentioning that the Api.create_message methods take the new `poll` attribute.

lib/nostrum/api.ex

@@ -219,8 +219,9 @@ defmodule Nostrum.Api do
     * `:embeds` (`t:Nostrum.Struct.Embed.t/0`) - a list of embedded rich content
     * `:allowed_mentions` (`t:allowed_mentions/0`) - see the allowed mentions type documentation
     * `:message_reference` (`map`) - See "Message references" below
+    * `:poll` (`t:Nostrum.Struct.Message.Poll.t/0`) - A poll object to send with the message
 
-    At least one of the following is required: `:content`, `:file`, `:embeds`.
+    At least one of the following is required: `:content`, `:file`, `:embeds`, `:poll`.
 
   ### Message reference
 

lib/nostrum/struct/message.ex

@@ -16,7 +16,8 @@ defmodule Nostrum.Struct.Message do
     Component,
     Reaction,
     Reference,
-    Sticker
+    Sticker,
+    Poll
   }
 
   alias Nostrum.{Snowflake, Util}
@@ -43,6 +44,7 @@ defmodule Nostrum.Struct.Message do
     :message_reference,
     :nonce,
     :pinned,
+    :poll,
     :reactions,
     :referenced_message,
     :sticker_items,
@@ -113,6 +115,9 @@ defmodule Nostrum.Struct.Message do
   """
   @type interaction :: Interaction.t()
 
+  @typedoc "The poll object attached to the message"
+  @type poll :: Poll.t()
+
   @typedoc "List of embedded content in the message"
   @type embeds :: [Embed.t()]
 
@@ -217,6 +222,7 @@ defmodule Nostrum.Struct.Message do
           message_reference: message_reference,
           nonce: nonce,
           pinned: pinned,
+          poll: poll,
           reactions: reactions,
           referenced_message: referenced_message,
           sticker_items: sticker_items,
@@ -250,6 +256,7 @@ defmodule Nostrum.Struct.Message do
       |> Map.update(:mentions, nil, &Util.cast(&1, {:list, {:struct, User}}))
       |> Map.update(:message_reference, nil, &Util.cast(&1, {:struct, Reference}))
       |> Map.update(:nonce, nil, &Util.cast(&1, Snowflake))
+      |> Map.update(:poll, nil, &Util.cast(&1, {:struct, Poll}))
       |> Map.update(:reactions, nil, &Util.cast(&1, {:list, {:struct, Reaction}}))
       |> Map.update(:referenced_message, nil, &Util.cast(&1, {:struct, __MODULE__}))
       |> Map.update(:sticker_items, nil, &Util.cast(&1, {:list, {:struct, Sticker}}))