docs(all): standardizes and adds return types, also some param fixes

src/plugins/httpd.ts

@@ -35,6 +35,7 @@ export class Httpd {
    * Starts a web server.
    * @returns {Observable<string>} Returns an Observable. Subscribe to receive the URL for your web server (if succeeded). Unsubscribe to stop the server.
    * @param options {HttpdOptions}
+   * @returns {Observable<string>}
    */
   @Cordova({
     observable: true,