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/AxiosURLSearchParams.js

@@ -1,6 +1,6 @@
 'use strict';
 
-var toFormData = require('./toFormData');
+import toFormData from './toFormData.js';
 
 /**
  * It encodes a string by replacing all characters that are not in the unreserved set with
@@ -11,7 +11,7 @@ var toFormData = require('./toFormData');
  * @returns {string} The encoded string.
  */
 function encode(str) {
-  var charMap = {
+  const charMap = {
     '!': '%21',
     "'": '%27',
     '(': '%28',
@@ -20,7 +20,7 @@ function encode(str) {
     '%20': '+',
     '%00': '\x00'
   };
-  return encodeURIComponent(str).replace(/[!'\(\)~]|%20|%00/g, function replacer(match) {
+  return encodeURIComponent(str).replace(/[!'()~]|%20|%00/g, function replacer(match) {
     return charMap[match];
   });
 }
@@ -39,14 +39,14 @@ function AxiosURLSearchParams(params, options) {
   params && toFormData(params, this, options);
 }
 
-var prototype = AxiosURLSearchParams.prototype;
+const prototype = AxiosURLSearchParams.prototype;
 
 prototype.append = function append(name, value) {
   this._pairs.push([name, value]);
 };
 
 prototype.toString = function toString(encoder) {
-  var _encode = encoder ? function(value) {
+  const _encode = encoder ? function(value) {
     return encoder.call(this, value, encode);
   } : encode;
 
@@ -55,4 +55,4 @@ prototype.toString = function toString(encoder) {
   }, '').join('&');
 };
 
-module.exports = AxiosURLSearchParams;
+export default AxiosURLSearchParams;