Add types to generate (#182)

* add type

* fix callback type

* callnback is optional

index.d.ts

@@ -0,0 +1,19 @@
+interface Options {
+  theme: string,
+  jsonFile: string,
+  jsonDir?: string, 
+  output: string,
+  screenshotsDirectory?: string,
+  reportSuiteAsScenarios: boolean,
+  ignoreBadJsonFile?: boolean,
+  launchReport: boolean,
+  columnLayout?: number,
+  storeScreenshots?: boolean,
+  noInlineScreenshots?: boolean,
+  name?: string,
+  metadata?: {
+    [key: string]: string
+  },
+}
+
+export function generate(options: Options, callback?: () => void): void

package.json

@@ -3,6 +3,7 @@
   "version": "5.0.0",
   "description": "Generates Cucumber HTML reports in three different themes",
   "main": "index.js",
+  "typings": "./index.d.ts",
   "author": {
     "name": "Kushang Gajjar",
     "email": "g.kushang@gmail.com"