Made demo files into typescript files

demo/demo13.ts

@@ -0,0 +1,28 @@
+// This example shows 3 styles using XML styles
+// Import from 'docx' rather than '../build' if you install from npm
+import * as fs from "fs";
+import { Document, Packer, Paragraph } from "../build";
+
+const styles = fs.readFileSync("./demo/assets/custom-styles.xml", "utf-8");
+const doc = new Document({
+    title: "Title",
+    externalStyles: styles,
+});
+
+doc.createParagraph("Cool Heading Text").heading1();
+
+const paragraph = new Paragraph('This is a custom named style from the template "MyFancyStyle"');
+paragraph.style("MyFancyStyle");
+doc.addParagraph(paragraph);
+
+doc.createParagraph("Some normal text");
+
+doc.createParagraph("MyFancyStyle again").style("MyFancyStyle");
+paragraph.style("MyFancyStyle");
+doc.addParagraph(paragraph);
+
+const packer = new Packer();
+
+packer.toBuffer(doc).then((buffer) => {
+    fs.writeFileSync("My Document.docx", buffer);
+});