Add Typescript typings

Author: Josh Woodcock

README.md

@@ -33,6 +33,7 @@ an error and the second being the successfully validated SNS message.
 The message validator checks the `SigningCertURL`, `SignatureVersion`, and
 `Signature` to make sure they are valid and consistent with the message data.
 
+#### Javascript
 ```javascript
 var MessageValidator = require('sns-validator'),
     validator = new MessageValidator();
@@ -47,6 +48,21 @@ validator.validate(message, function (err, message) {
 });
 ```
 
+#### Typescript
+```typescript
+import { MessageValidator } from "sns-validator"
+const validator = new MessageValidator();
+
+validator.validate(message, function (err, message) {
+    if (err) {
+        // Your message could not be validated.
+        return;
+    }
+
+    // message has been validated and its signature checked.
+});
+```
+
 ## Installation
 
 The SNS Message Validator relies on the Node crypto module and is only designed

index.d.ts

@@ -0,0 +1,4 @@
+export declare class MessageValidator {
+    encoding: string;
+    validate(hash: any, cb: (err: string, message: string) => any);
+}

index.js

@@ -213,4 +213,6 @@ MessageValidator.prototype.validate = function (hash, cb) {
     validateSignature(hash, cb, this.encoding);
 };
 
+MessageValidator.MessageValidator = MessageValidator;
+
 module.exports = MessageValidator;