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/utils/extend.spec.js

@@ -1,18 +1,20 @@
-var extend = require('../../../lib/utils').extend;
+import utils from '../../../lib/utils';
+
+const {extend} = utils;
 
 describe('utils::extend', function () {
   it('should be mutable', function () {
-    var a = {};
-    var b = {foo: 123};
+    const a = {};
+    const b = {foo: 123};
 
     extend(a, b);
 
     expect(a.foo).toEqual(b.foo);
   });
-  
+
   it('should extend properties', function () {
-    var a = {foo: 123, bar: 456};
-    var b = {bar: 789};
+    let a = {foo: 123, bar: 456};
+    const b = {bar: 789};
 
     a = extend(a, b);
 
@@ -21,9 +23,9 @@ describe('utils::extend', function () {
   });
 
   it('should bind to thisArg', function () {
-    var a = {};
-    var b = {getFoo: function getFoo() { return this.foo; }};
-    var thisArg = { foo: 'barbaz' };
+    const a = {};
+    const b = {getFoo: function getFoo() { return this.foo; }};
+    const thisArg = { foo: 'barbaz' };
 
     extend(a, b, thisArg);