add TypeScript support

graceful.d.ts

@@ -0,0 +1,21 @@
+type SignalListener = (done: () => void, event: any, signal: string) => (undefined | Promise)
+type cancelSubscription = () => void
+
+
+export declare module Graceful {
+    let exitOnDouble: boolean;
+    let timeout: number;
+
+    function on(event: string, listener: Function, deadly?: boolean): cancelSubscription;
+    function on(event: "SIGTERM", listener: SignalListener, deadly?: boolean): cancelSubscription;
+    function on(event: "SIGINT", listener: SignalListener, deadly?: boolean): cancelSubscription;
+    function on(event: "SIGBREAK", listener: SignalListener, deadly?: boolean): cancelSubscription;
+    function on(event: "SIGHUP", listener: SignalListener, deadly?: boolean): cancelSubscription;
+    function on(event: "exit", listener: SignalListener, deadly?: boolean): cancelSubscription;
+
+    function off(event: string, listener: Function): void;
+
+    function clear(signal?: string): void;
+
+    function exit(code?: number | string, signal?: string): void;
+}