Add math run and fraction

src/file/paragraph/math/math-run.ts

@@ -0,0 +1,11 @@
+import { XmlComponent } from "file/xml-components";
+
+import { MathText } from "./math-text";
+
+export class MathRun extends XmlComponent {
+    constructor(readonly text: string) {
+        super("m:r");
+
+        this.root.push(new MathText(text));
+    }
+}