Add features: custom server and websocket. Minor refactoring

examples/websocket/bunext.config.ts

@@ -0,0 +1,8 @@
+import type { BunextConfig } from "../../dist/types";
+import { BunextWebsocket } from "./websocket";
+
+const config: BunextConfig = {
+    websocket: BunextWebsocket,
+};
+
+export default config;