Adding typescript definitions

package.json

@@ -4,6 +4,7 @@
   "description": "helpers for getting webpack bundles to be loaded by systemjs",
   "main": "src/webpack-config-helpers.js",
   "module": "src/systemjs-webpack-interop.js",
+  "types": "src/systemjs-webpack-interop.d.ts",
   "repository": "https://github.com/joeldenning/systemjs-webpack-interop.git",
   "author": "Joel Denning <joeldenning@gmail.com>",
   "license": "MIT",

src/systemjs-webpack-interop.d.ts

@@ -0,0 +1,15 @@
+declare module "systemjs-webpack-interop" {
+  export function setPublicPath(
+    moduleName: string,
+    rootDirectoryLevel?: number
+  ): void;
+  export function modifyWebpackConfig(
+    webpackConfig: WebpackConfig
+  ): WebpackConfig;
+  export function verifyWebpackConfig(webpackConfig): void;
+
+  type WebpackConfig = object | WebpackConfigGetter;
+  interface WebpackConfigGetter {
+    (): void;
+  }
+}