Add User.lastMessage, GuildMember.lastMessage and TextBasedChannel.lastMessage (#1135)

* Add User.lastMessage

* User.lastMessage and GuildMember.lastMessage

* User, GuildMember and TextBasedChannel lastMessage

* Update MessageCreate.js

src/structures/GuildMember.js

@@ -39,6 +39,12 @@ class GuildMember {
      * @type {?Snowflake}
      */
     this.lastMessageID = null;
+
+    /**
+     * The Message object of the last message sent by the member in their guild, if one was sent.
+     * @type {?Message}
+     */
+    this.lastMessage = null;
   }
 
   setup(data) {

src/structures/User.js

@@ -55,6 +55,12 @@ class User {
      * @type {?Snowflake}
      */
     this.lastMessageID = null;
+
+    /**
+     * The Message object of the last message sent by the user, if one was sent.
+     * @type {?Message}
+     */
+    this.lastMessage = null;
   }
 
   patch(data) {

src/structures/interface/TextBasedChannel.js

@@ -20,6 +20,12 @@ class TextBasedChannel {
      * @type {?Snowflake}
      */
     this.lastMessageID = null;
+
+    /**
+     * The Message object of the last message in the channel, if one was sent.
+     * @type {?Message}
+     */
+    this.lastMessage = null;
   }
 
   /**