Added setTopic implementation

lib/Client/InternalClient.js

@@ -729,6 +729,34 @@ var InternalClient = (function () {
 		});
 	};
 
+	//def setTopic
+
+	InternalClient.prototype.setTopic = function setTopic(chann) {
+		var topic = arguments.length <= 1 || arguments[1] === undefined ? "" : arguments[1];
+
+		var self = this;
+		return new Promise(function (resolve, reject) {
+
+			self.resolver.resolveChannel(chann).then(next)["catch"](reject);
+
+			function next(channel) {
+
+				request.patch(Endpoints.CHANNEL(channel.id)).set("authorization", self.token).send({
+					name: channel.name,
+					position: 0,
+					topic: topic
+				}).end(function (err, res) {
+					if (err) {
+						reject(err);
+					} else {
+						channel.topic = res.body.topic;
+						resolve();
+					}
+				});
+			}
+		});
+	};
+
 	InternalClient.prototype.sendWS = function sendWS(object) {
 		if (this.websocket) this.websocket.send(JSON.stringify(object));
 	};