Initial SNBT implementation

lib/nbt/Stream.dart

@@ -377,3 +377,22 @@ class ByteLayer {
     setBit(position, maskToSet);
   }
 }
+
+class StringBuilder {
+  String _buffer = "";
+
+  StringBuilder();
+
+  void append(String value) {
+    _buffer += value;
+  }
+
+  void clear() {
+    _buffer = "";
+  }
+
+  @override
+  String toString() {
+    return "${_buffer}";
+  }
+}