feature: teams support (#3350)

* basic teams support

* export Team & TeamMember

* use typedef

* typings and some fixes

* Update src/structures/TeamMember.js

Co-Authored-By: Vlad Frangu <kingdgrizzle@gmail.com>

* fix Team#iconURL()

* fix typings and a bug

* fix states start at 1

* team icon hash can be null

* fix owner typings

src/structures/TeamMember.js

@@ -0,0 +1,62 @@
+'use strict';
+
+const Base = require('./Base');
+const { MembershipStates } = require('../util/Constants');
+
+/**
+ * Represents a Client OAuth2 Application Team Member.
+ * @extends {Base}
+ */
+class TeamMember extends Base {
+  constructor(client, team, data) {
+    super(client);
+
+    /**
+     * The Team this member is part of
+     * @type {Team}
+     */
+    this.team = team;
+
+    this._patch(data);
+  }
+
+  _patch(data) {
+    /**
+     * The permissions this Team Member has with reguard to the team
+     * @type {string[]}
+     */
+    this.permissions = data.permissions;
+
+    /**
+     * The permissions this Team Member has with reguard to the team
+     * @type {MembershipStates}
+     */
+    this.membershipState = MembershipStates[data.membership_state];
+
+    /**
+     * The user for this Team Member
+     * @type {User}
+     */
+    this.user = this.client.users.add(data.user);
+
+    /**
+     * The ID of the Team Member
+     * @type {Snowflake}
+     */
+    this.id = this.user.id;
+  }
+
+  /**
+   * When concatenated with a string, this automatically returns the team members's tag instead of the
+   * TeamMember object.
+   * @returns {string}
+   * @example
+   * // Logs: Team Member's tag: @Hydrabolt
+   * console.log(`Team Member's tag: ${teamMember}`);
+   */
+  toString() {
+    return this.user.toString();
+  }
+}
+
+module.exports = TeamMember;