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/module/cjs/index.js

@@ -0,0 +1,11 @@
+const axios = require('axios');
+const assert = require('assert');
+
+const {CanceledError, AxiosError, AxiosHeaders} = axios;
+
+assert.strictEqual(typeof axios, 'function');
+assert.strictEqual(typeof CanceledError, 'function');
+assert.strictEqual(typeof AxiosError, 'function');
+assert.strictEqual(typeof AxiosHeaders, 'function');
+
+console.log('CommonJS importing test passed');