Add pinning (#434)

Added methods:
pinMessage()
unpinMessage()
getPinnedMessages()

Added params for getChannelLogs:
around

lib/Client/Client.js

@@ -544,6 +544,94 @@ var Client = (function (_EventEmitter) {
 		return this.internal.getMessage(channel, messageID).then(dataCallback(callback), errorCallback(callback));
 	};
 
+	/**
+  * Pins a message to a channel.
+  * @param {MessageResolvable} message to pin.
+  * @returns {Promise<null, Error>} resolves null if successful, otherwise rejects with an error.
+  * @example
+  * // pin message - callback
+  * client.pinMessage(msg, (err) => {
+  *     if(!err) {
+  *         console.log("Successfully pinned message")
+  *     } else {
+  *         console.log("Couldn't pin the message: " + err);
+  *     }
+  * });
+  * @example
+  * // pin message - promise
+  * client.pinMessage(msg)
+  *     .then(() => {
+  *         console.log("Successfully pinned message");
+  *     })
+  *     .catch(err => console.log("Couldn't pin the message: " + err));
+  */
+
+	Client.prototype.pinMessage = function pinMessage(msg) {
+		var callback = arguments.length <= 1 || arguments[1] === undefined ? function () /*err*/{} : arguments[1];
+
+		return this.internal.pinMessage(msg).then(dataCallback(callback), errorCallback(callback));
+	};
+
+	/**
+  * Unpins a message to a server.
+  * @param {MessageResolvable} message to unpin.
+  * @returns {Promise<null, Error>} resolves null if successful, otherwise rejects with an error.
+  * @example
+  * // unpin message - callback
+  * client.unpinMessage(msg, (err) => {
+  *     if(!err) {
+  *         console.log("Successfully unpinned message")
+  *     } else {
+  *         console.log("Couldn't pin the message: " + err);
+  *     }
+  * });
+  * @example
+  * // unpin message - promise
+  * client.unpinMessage(msg)
+  *     .then(() => {
+  *         console.log("Successfully unpinned message");
+  *     })
+  *     .catch(err => console.log("Couldn't unpin the message: " + err));
+  */
+
+	Client.prototype.unpinMessage = function unpinMessage(msg) {
+		var callback = arguments.length <= 1 || arguments[1] === undefined ? function () /*err*/{} : arguments[1];
+
+		return this.internal.unpinMessage(msg).then(dataCallback(callback), errorCallback(callback));
+	};
+
+	/**
+  * Gets all pinned messages of a channel.
+  * @param {TextChannelResolvable} where to get the pins from.
+  * @returns {Promise<Array<Message>, Error>} Resolves with an array of messages if successful, otherwise rejects with an error.
+  * @example
+  * // log all pinned messages - callback
+  * client.getPinnedMessages(channel, (err, messages) => {
+  *     if(!err) {
+  *         for(var message of messages) {
+  *             console.log(message.content);
+  *         }
+  *     } else {
+  *         console.log("Couldn't fetch pins: " + err);
+  *     }
+  * });
+  * @example
+  * // log all pinned messages - promise
+  * client.getPinnedMessages(channel)
+  *     .then(messages => {
+  *         for(var message of messages) {
+  *             console.log(message.content);
+  *         }
+  *     })
+  *     .catch(err => console.log("Couldn't fetch pins: " + err));
+  */
+
+	Client.prototype.getPinnedMessages = function getPinnedMessages(channel) {
+		var callback = arguments.length <= 1 || arguments[1] === undefined ? function () /*err, messages*/{} : arguments[1];
+
+		return this.internal.getPinnedMessages(channel).then(dataCallback(callback), errorCallback(callback));
+	};
+
 	/**
   * Gets the banned users of a server (if the client has permission to)
   * @param {ServerResolvable} server server to get banned users of