Move FormatDurationOptions under namespace formatDuration (#20)

resolves #19

Author: sebinemeth

format-duration.d.ts

@@ -1,18 +1,22 @@
-export interface FormatDurationOptions {
-  /**
-   * Adds leading zero to the formatted string.
-   */
-  leading?: boolean
-  ms?: boolean
+declare namespace formatDuration {
+  interface FormatDurationOptions {
+    /**
+     * Adds leading zero to the formatted string.
+     */
+    leading?: boolean
+    ms?: boolean
+  }
 }
 
 /**
- * Convert a number in milliseconds to a standard duration string.
- *
- * @param {number} ms The number to format.
- * @param {object} options - Formatting options
- * @returns {string} The formatted duration string.
- */
-declare function formatDuration (ms: number, options?: FormatDurationOptions): string
-
+  * Convert a number in milliseconds to a standard duration string.
+  * 
+  * @param {number} ms The number to format.
+  * @param {object} options - Formatting options
+  * @returns {string} The formatted duration string.
+  */
+declare function formatDuration(
+  ms: number,
+  options?: formatDuration.FormatDurationOptions
+): string
 export = formatDuration