Consider using function to check type of variable

I think we should we function to check type of variable like underscore or lodash to make it more flexible or easier to test

Author: MQuy

CCBoot.js

@@ -103,6 +103,63 @@ cc.extend = function(target) {
     return target;
 };
 
+/**
+ * Check the obj whether is function or not
+ * @param {*} obj
+ * @returns {boolean}
+ */
+cc.isFunction = function(obj) {
+    return typeof obj == 'function';
+};
+
+/**
+ * Check the obj whether is number or not
+ * @param {*} obj
+ * @returns {boolean}
+ */
+cc.isNumber = function(obj) {
+    return typeof obj == 'number' || Object.prototype.toString.call(obj) == '[object Number]';
+};
+
+/**
+ * Check the obj whether is string or not
+ * @param {*} obj
+ * @returns {boolean}
+ */
+cc.isString = function(obj) {
+    return typeof obj == 'string' || Object.prototype.toString.call(obj) == '[object String]';
+};
+
+/**
+ * Check the obj whether is array or not
+ * @param {*} obj
+ * @returns {boolean}
+ */
+cc.isArray = function(obj) {
+    return Object.prototype.toString.call(obj) == '[object Array]';
+};
+
+/**
+ * Check the obj whether is undefined or not
+ * @param {*} obj
+ * @returns {boolean}
+ */
+
+cc.isUndefined = function(obj) {
+    return typeof obj == 'undefined';
+};
+
+/**
+ * Check the obj whether is object or not
+ * @param {*} obj
+ * @returns {boolean}
+ */
+cc.isObject = function(obj) {
+    var type = typeof obj;
+
+    return type == 'function' || (obj && type == 'object');
+}
+
 /**
  * Check the url whether cross origin
  * @param {String} url