Add directive observable

Author: dolanmiu

my-typings/avs/directives.d.ts

@@ -0,0 +1,3 @@
+declare namespace AVS {
+    type Directive = AVS.SpeechRecognizer.ExpectSpeechDirective | AVS.AudioPlayer.PlayDirective;
+}

src/directives.ts

@@ -1,9 +1,12 @@
 // https://developer.amazon.com/docs/alexa-voice-service/manage-http2-connection.html
 import * as http2 from "http2";
+import {Observable} from "rxjs/Observable";
 
 import {API_VERSION} from "./constants/general";
 
 export default class Directives {
+    private directive$: Observable<AVS.Directive>;
+
     constructor(private readonly client: http2.ClientHttp2Session) {}
 
     public connect(accessToken: string): Promise<void> {
@@ -39,4 +42,8 @@ export default class Directives {
             req.end();
         });
     }
+
+    public get Directive$(): Observable<AVS.Directive> {
+        return this.directive$;
+    }
 }