Forgot a few minor things about packaging for use inside other projects 😀. Should be good now though.

src/index.ts

@@ -0,0 +1,15 @@
+import { API, APICredentials } from './API';
+import { Campaign } from './Campaign';
+import { Template } from './Template';
+import { Subscriber } from './Subscriber';
+import { List } from './List';
+
+
+export {
+    API,
+    APICredentials,
+    Campaign,
+    Template,
+    Subscriber,
+    List
+}

tsconfig.json

@@ -50,7 +50,7 @@
     // "maxNodeModuleJsDepth": 1,                        /* Specify the maximum folder depth used for checking JavaScript files from 'node_modules'. Only applicable with 'allowJs'. */
 
     /* Emit */
-    // "declaration": true,                              /* Generate .d.ts files from TypeScript and JavaScript files in your project. */
+    "declaration": true,                              /* Generate .d.ts files from TypeScript and JavaScript files in your project. */
     // "declarationMap": true,                           /* Create sourcemaps for d.ts files. */
     // "emitDeclarationOnly": true,                      /* Only output d.ts files and not JavaScript files. */
     // "sourceMap": true,                                /* Create source map files for emitted JavaScript files. */