Add PureJSON renderer (#694)

Closes #693

render/render_17_test.go

@@ -0,0 +1,26 @@
+// Copyright 2018 Gin Core Team.  All rights reserved.
+// Use of this source code is governed by a MIT style
+// license that can be found in the LICENSE file.
+
+// +build go1.7
+
+package render
+
+import (
+	"net/http/httptest"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestRenderPureJSON(t *testing.T) {
+	w := httptest.NewRecorder()
+	data := map[string]interface{}{
+		"foo":  "bar",
+		"html": "<b>",
+	}
+	err := (PureJSON{data}).Render(w)
+	assert.NoError(t, err)
+	assert.Equal(t, "{\"foo\":\"bar\",\"html\":\"<b>\"}\n", w.Body.String())
+	assert.Equal(t, "application/json; charset=utf-8", w.Header().Get("Content-Type"))
+}