Axios ES2017 (#4787)

* Added AxiosHeaders class;

* Fixed README.md href;

* Fixed a potential bug with headers normalization;

* Fixed a potential bug with headers normalization;
Refactored accessor building routine;
Refactored default transforms;
Removed `normalizeHeaderName` helper;

* Added `Content-Length` accessor;
Added missed `has` accessor to TS types;

* Added `AxiosTransformStream` class;
Added progress capturing ability for node.js environment;
Added `maxRate` option to limit the data rate in node.js environment;
Refactored event handled by `onUploadProgress` && `onDownloadProgress` listeners in browser environment;
Added progress & data rate tests for the http adapter;
Added response stream aborting test;
Added a manual progress capture test for the browser;
Updated TS types;
Added TS tests;
Refactored request abort logic for the http adapter;
Added ability to abort the response stream;

* Remove `stream/promises` & `timers/promises` modules usage in tests;

* Use `abortcontroller-polyfill`;

* Fixed AxiosTransformStream dead-lock in legacy node versions;
Fixed CancelError emitting in streams;

* Reworked AxiosTransformStream internal logic to optimize memory consumption;
Added throwing an error if the request stream was silently destroying (without error) Refers to #3966;

* Treat the destruction of the request stream as a cancellation of the request;
Fixed tests;

* Emit `progress` event in the next tick;

* Initial refactoring;

* Refactored Mocha tests to use ESM;

* Refactored Karma tests to use rollup preprocessor & ESM;
Replaced grunt with gulp;
Improved dev scripts;
Added Babel for rollup build;

* Added default commonjs package export for Node build;
Added automatic contributors list generator for package.json;

Co-authored-by: Jay <jasonsaayman@gmail.com>

lib/helpers/validator.js

@@ -1,18 +1,18 @@
 'use strict';
 
-var VERSION = require('../env/data').version;
-var AxiosError = require('../core/AxiosError');
+import {VERSION} from '../env/data.js';
+import AxiosError from '../core/AxiosError.js';
 
-var validators = {};
+const validators = {};
 
 // eslint-disable-next-line func-names
-['object', 'boolean', 'number', 'function', 'string', 'symbol'].forEach(function(type, i) {
+['object', 'boolean', 'number', 'function', 'string', 'symbol'].forEach((type, i) => {
   validators[type] = function validator(thing) {
     return typeof thing === type || 'a' + (i < 1 ? 'n ' : ' ') + type;
   };
 });
 
-var deprecatedWarnings = {};
+const deprecatedWarnings = {};
 
 /**
  * Transitional option validator
@@ -29,7 +29,7 @@ validators.transitional = function transitional(validator, version, message) {
   }
 
   // eslint-disable-next-line func-names
-  return function(value, opt, opts) {
+  return (value, opt, opts) => {
     if (validator === false) {
       throw new AxiosError(
         formatMessage(opt, ' has been removed' + (version ? ' in ' + version : '')),
@@ -66,14 +66,14 @@ function assertOptions(options, schema, allowUnknown) {
   if (typeof options !== 'object') {
     throw new AxiosError('options must be an object', AxiosError.ERR_BAD_OPTION_VALUE);
   }
-  var keys = Object.keys(options);
-  var i = keys.length;
+  const keys = Object.keys(options);
+  let i = keys.length;
   while (i-- > 0) {
-    var opt = keys[i];
-    var validator = schema[opt];
+    const opt = keys[i];
+    const validator = schema[opt];
     if (validator) {
-      var value = options[opt];
-      var result = value === undefined || validator(value, opt, options);
+      const value = options[opt];
+      const result = value === undefined || validator(value, opt, options);
       if (result !== true) {
         throw new AxiosError('option ' + opt + ' must be ' + result, AxiosError.ERR_BAD_OPTION_VALUE);
       }
@@ -85,7 +85,7 @@ function assertOptions(options, schema, allowUnknown) {
   }
 }
 
-module.exports = {
-  assertOptions: assertOptions,
-  validators: validators
+export default {
+  assertOptions,
+  validators
 };