Added basic openapi support

ref #5

src/loaders/openapi.ts

@@ -0,0 +1,11 @@
+import { Application } from "express";
+import * as swaggerUiExpress from "swagger-ui-express";
+import { getMetadataArgsStorage } from "routing-controllers";
+import { routingControllersToSpec } from "routing-controllers-openapi";
+
+export default async (app: Application) => {
+    const storage = getMetadataArgsStorage();
+    const spec = routingControllersToSpec(storage);
+    app.use("/docs", swaggerUiExpress.serve, swaggerUiExpress.setup(spec));
+    return app;
+};