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>

sandbox/server.js

@@ -1,8 +1,8 @@
-var fs = require('fs');
-var url = require('url');
-var path = require('path');
-var http = require('http');
-var server;
+import fs from 'fs';
+import url from 'url';
+import path from 'path';
+import http from 'http';
+let server;
 
 function pipeFileToResponse(res, file, type) {
   if (type) {
@@ -17,8 +17,8 @@ function pipeFileToResponse(res, file, type) {
 server = http.createServer(function (req, res) {
   req.setEncoding('utf8');
 
-  var parsed = url.parse(req.url, true);
-  var pathname = parsed.pathname;
+  const parsed = url.parse(req.url, true);
+  let pathname = parsed.pathname;
 
   console.log('[' + new Date() + ']', req.method, pathname);
 
@@ -33,9 +33,9 @@ server = http.createServer(function (req, res) {
   } else if (pathname === '/axios.map') {
     pipeFileToResponse(res, '../dist/axios.map', 'text/javascript');
   } else if (pathname === '/api') {
-    var status;
-    var result;
-    var data = '';
+    let status;
+    let result;
+    let data = '';
 
     req.on('data', function (chunk) {
       data += chunk;