Add more methods and singleton

src/api/api.base.ts

@@ -66,7 +66,7 @@ export abstract class TribufuApiBase {
      */
     protected static defaultHeaders(): HttpHeaders {
         const headers = {};
-        headers["X-Tribufu-Language"] = "javascript";
+        headers["X-Tribufu-Library"] = "javascript";
         headers["X-Tribufu-Version"] = TRIBUFU_VERSION;
         return headers;
     }

src/api/singletion.ts

@@ -0,0 +1,23 @@
+// Copyright (c) Tribufu. All Rights Reserved.
+// SPDX-License-Identifier: MIT
+
+import { TribufuApi } from "./index";
+
+/**
+ * **Tribufu API**
+ *
+ * Helper class to get a singleton instance of the Tribufu API.
+ */
+export class TribufuApiSingleton {
+    private static INSTANCE: TribufuApi | null = null;
+
+    private constructor() {}
+
+    public static getInstance(): TribufuApi {
+        if (!TribufuApiSingleton.INSTANCE) {
+            TribufuApiSingleton.INSTANCE = TribufuApi.fromEnvOrDefault();
+        }
+
+        return TribufuApiSingleton.INSTANCE;
+    }
+}