Refactored module exports; (#5162)

* Refactored build pipeline;
Added module exports tests;
Added missing ESM export for parity with Axios factory;
Added `toFormData`, `formToJSON`, `isAxiosError`, `spread`, `isCancel`, `all` as named export to `index.d.ts`;

* Added ESM entry test;

* Updated README.md `installing` section;

* Added TypeScript importing test;
Added missed `CanceledError` & `AxiosHeaders` to `AxiosStatic` interface;

* Exclude `/test/module/` from tslint;

test/specs/instance.spec.js

@@ -26,7 +26,8 @@ describe('instance', function () {
         'VERSION',
         'default',
         'toFormData',
-        'formToJSON'
+        'formToJSON',
+        'AxiosHeaders'
       ].indexOf(prop) > -1) {
         continue;
       }