i18n: expose the LoaderConfig from the main i18n instance and add an example

Signed-off-by: Gerasimos (Makis) Maropoulos <kataras2006@hotmail.com>

_examples/i18n/i18n-template/main_test.go

@@ -0,0 +1,17 @@
+package main
+
+import (
+	"testing"
+
+	"github.com/kataras/iris/v12/httptest"
+)
+
+func TestI18nLoaderFuncMap(t *testing.T) {
+	app := newApp()
+
+	e := httptest.New(t, app)
+	e.GET("/").Expect().Status(httptest.StatusOK).
+		Body().Equal("Hi 2 dogs")
+	e.GET("/").WithHeader("Accept-Language", "el").Expect().Status(httptest.StatusOK).
+		Body().Equal("Γειά 2 σκυλί")
+}