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>

test/specs/core/settle.spec.js

@@ -1,8 +1,8 @@
-var settle = require('../../../lib/core/settle');
+import settle from '../../../lib/core/settle';
 
 describe('core::settle', function() {
-  var resolve;
-  var reject;
+  let resolve;
+  let reject;
 
   beforeEach(function() {
     resolve = jasmine.createSpy('resolve');
@@ -10,7 +10,7 @@ describe('core::settle', function() {
   });
 
   it('should resolve promise if status is not set', function() {
-    var response = {
+    const response = {
       config: {
         validateStatus: function() {
           return true;
@@ -23,7 +23,7 @@ describe('core::settle', function() {
   });
 
   it('should resolve promise if validateStatus is not set', function() {
-    var response = {
+    const response = {
       status: 500,
       config: {
       }
@@ -34,7 +34,7 @@ describe('core::settle', function() {
   });
 
   it('should resolve promise if validateStatus returns true', function() {
-    var response = {
+    const response = {
       status: 500,
       config: {
         validateStatus: function() {
@@ -48,10 +48,10 @@ describe('core::settle', function() {
   });
 
   it('should reject promise if validateStatus returns false', function() {
-    var req = {
+    const req = {
       path: '/foo'
     };
-    var response = {
+    const response = {
       status: 500,
       config: {
         validateStatus: function() {
@@ -63,7 +63,7 @@ describe('core::settle', function() {
     settle(resolve, reject, response);
     expect(resolve).not.toHaveBeenCalled();
     expect(reject).toHaveBeenCalled();
-    var reason = reject.calls.first().args[0];
+    const reason = reject.calls.first().args[0];
     expect(reason instanceof Error).toBe(true);
     expect(reason.message).toBe('Request failed with status code 500');
     expect(reason.config).toBe(response.config);
@@ -72,8 +72,8 @@ describe('core::settle', function() {
   });
 
   it('should pass status to validateStatus', function() {
-    var validateStatus = jasmine.createSpy('validateStatus');
-    var response = {
+    const validateStatus = jasmine.createSpy('validateStatus');
+    const response = {
       status: 500,
       config: {
         validateStatus: validateStatus