Use a Renderer interface instead of rendering fragments

heading.go

@@ -0,0 +1,26 @@
+package gold
+
+import (
+	"fmt"
+	"io"
+	"strings"
+
+	bf "gopkg.in/russross/blackfriday.v2"
+)
+
+type HeadingElement struct {
+}
+
+func (e *HeadingElement) Render(w io.Writer, node *bf.Node, tr *TermRenderer) error {
+	var pre string
+	if node.Prev != nil {
+		pre = "\n"
+	}
+
+	el := &BaseElement{
+		Pre:   pre,
+		Token: fmt.Sprintf("%s %s", strings.Repeat("#", node.HeadingData.Level), node.FirstChild.Literal),
+		Style: Heading,
+	}
+	return el.Render(w, node, tr)
+}