Allow creating Styles and assigning them to File.Styles

Closes #109

demo/demo27.ts

@@ -0,0 +1,34 @@
+import * as fs from "fs";
+import { Document, Packer } from "../build";
+
+const doc = new Document();
+const myStyles = doc.Styles;
+
+// The first argument is an ID you use to apply the style to paragraphs
+// The second argument is a human-friendly name to show in the UI
+myStyles.createParagraphStyle("myWonkyStyle", "My Wonky Style")
+    .basedOn("Normal")
+    .next("Normal")
+    .color("990000")
+    .italics()
+    .indent({left: 720})  // 720 TWIP === 720 / 20 pt === .5 in
+    .spacing({line: 276});  // 276 / 240 = 1.15x line spacing
+
+myStyles.createParagraphStyle("Heading2", "Heading 2")
+    .basedOn("Normal")
+    .next("Normal")
+    .quickFormat()
+    .size(26)  // 26 half-points === 13pt font
+    .bold()
+    .underline("double", "FF0000")
+    .spacing({before: 240, after: 120});  // TWIP for both
+
+doc.createParagraph("Hello").style("myWonkyStyle");
+doc.createParagraph("World").heading2(); // Uses the Heading2 style
+
+const packer = new Packer();
+
+packer.toBuffer(doc).then((buffer) => {
+    fs.writeFileSync("My Document.docx", buffer);
+    console.log("Document created successfully at project root!");
+});

src/file/document/index.ts

@@ -1,2 +1,3 @@
 export * from "./document";
+export * from "./document-attributes";
 export * from "./body";

src/file/file.ts

@@ -17,7 +17,7 @@ import { Table } from "./table";
 
 export class File {
     private readonly document: Document;
-    private readonly styles: Styles;
+    private styles: Styles;
     private readonly coreProperties: CoreProperties;
     private readonly numbering: Numbering;
     private readonly media: Media;
@@ -214,6 +214,10 @@ export class File {
         return this.styles;
     }
 
+    public set Styles(styles: Styles) {
+        this.styles = styles;
+    }
+
     public get CoreProperties(): CoreProperties {
         return this.coreProperties;
     }