Create NewGenerator and checks for the generator construct

generator.go

@@ -1,6 +1,10 @@
 package atomfeed
 
-import "errors"
+import (
+	"errors"
+	"fmt"
+	"html"
+)
 
 type Generator struct {
 	*CommonAttributes
@@ -9,10 +13,24 @@ type Generator struct {
 	Text    string `xml:"text"`
 }
 
+func NewGenerator(text string) *Generator {
+	return &Generator{Text: html.UnescapeString(text)}
+}
+
 func (g *Generator) Check() error {
+	if g.URI != "" {
+		if !isValidURI(g.URI) {
+			return fmt.Errorf("uri attribute %v of generator not correctly formatted", g.URI)
+		}
+	}
+
 	if g.Text == "" {
 		return errors.New("text element of generator empty")
 	}
 
+	if !isCorrectlyEscaped(g.Text) {
+		return fmt.Errorf("text element %v of generator not correctly escaped", g.Text)
+	}
+
 	return nil
 }