add core view extension with JTE and Thymeleaf support

flash-extensions/flash-ext-view-thymeleaf/docs/fragments.md

@@ -0,0 +1,16 @@
+# Fragments
+
+Use `@Fragment` for Thymeleaf fragment responses.
+
+```java
+@GET("/users/table")
+@Fragment(template = "fragments/users", value = "rows")
+public final class UsersRows extends ThymeleafHandler {
+    @Override
+    public ViewModel render(dev.relism.models.Request req) {
+        return ViewModel.of("users", List.of());
+    }
+}
+```
+
+If `value` is blank, runtime uses the configured default fragment (default: `content`).