Refactored AxiosError to a constructor;

Refactored `Cancel` to a constructor, a subclass of the `AxiosError`;
Expose CanceledError class;
Refactored axios error codes;
Added `toFlatObject` util;

lib/core/AxiosError.js

@@ -0,0 +1,86 @@
+'use strict';
+
+var utils = require('../utils');
+
+/**
+ * Create an Error with the specified message, config, error code, request and response.
+ *
+ * @param {string} message The error message.
+ * @param {string} [code] The error code (for example, 'ECONNABORTED').
+ * @param {Object} [config] The config.
+ * @param {Object} [request] The request.
+ * @param {Object} [response] The response.
+ * @returns {Error} The created error.
+ */
+function AxiosError(message, code, config, request, response) {
+  Error.call(this);
+  this.message = message;
+  this.name = 'AxiosError';
+  code && (this.code = code);
+  config && (this.config = config);
+  request && (this.request = request);
+  response && (this.response = response);
+}
+
+utils.inherits(AxiosError, Error, {
+  toJSON: function toJSON() {
+    return {
+      // Standard
+      message: this.message,
+      name: this.name,
+      // Microsoft
+      description: this.description,
+      number: this.number,
+      // Mozilla
+      fileName: this.fileName,
+      lineNumber: this.lineNumber,
+      columnNumber: this.columnNumber,
+      stack: this.stack,
+      // Axios
+      config: this.config,
+      code: this.code,
+      status: this.response && this.response.status ? this.response.status : null
+    };
+  }
+});
+
+var prototype = AxiosError.prototype;
+var descriptors = {};
+
+[
+  'ERR_BAD_OPTION_VALUE',
+  'ERR_BAD_OPTION',
+  'ECONNABORTED',
+  'ETIMEDOUT',
+  'ERR_NETWORK',
+  'ERR_FR_TOO_MANY_REDIRECTS',
+  'ERR_DEPRECATED',
+  'ERR_BAD_RESPONSE',
+  'ERR_BAD_REQUEST',
+  'ERR_CANCELED'
+// eslint-disable-next-line func-names
+].forEach(function(code) {
+  descriptors[code] = {value: code};
+});
+
+Object.defineProperties(AxiosError, descriptors);
+Object.defineProperty(prototype, 'isAxiosError', {value: true});
+
+// eslint-disable-next-line func-names
+AxiosError.from = function(error, code, config, request, response, customProps) {
+  var axiosError = Object.create(prototype);
+
+  utils.toFlatObject(error, axiosError, function filter(obj) {
+    return obj !== Error.prototype;
+  });
+
+  AxiosError.call(axiosError, error.message, code, config, request, response);
+
+  axiosError.name = error.name;
+
+  customProps && Object.assign(axiosError, customProps);
+
+  return axiosError;
+};
+
+module.exports = AxiosError;