add new feature to set progress callback

html2pdf_test.go

@@ -1,6 +1,7 @@
 package html2pdf
 
 import (
+	"fmt"
 	"os"
 	"path/filepath"
 	"strings"
@@ -46,6 +47,10 @@ func TestConvertFiles(t *testing.T) {
 		t.Fatal(err)
 	}
 
+	c.SetProgressCallback(func(progress int) {
+		fmt.Println(progress)
+	})
+
 	if err := c.Convert(input...); err != nil {
 		t.Fatal(err)
 	}