Add header objects and demo

demo/demo8.js

@@ -0,0 +1,12 @@
+const docx = require('../build');
+
+var doc = new docx.File();
+
+doc.createParagraph("Hello World");
+
+doc.Header.createParagraph("Header text");
+
+var exporter = new docx.LocalPacker(doc);
+exporter.pack('My Document');
+
+console.log('Document created succesfully at project root!');