added a way to customize headers used when connecting

Author: mackuba

lib/skyfall/stream.rb

@@ -181,7 +181,11 @@ def reconnect_delay
     end
 
     def build_websocket_client(url)
-      Faye::WebSocket::Client.new(url, nil, { headers: { 'User-Agent' => user_agent }})
+      Faye::WebSocket::Client.new(url, nil, { headers: { 'User-Agent' => user_agent }.merge(request_headers) })
+    end
+
+    def request_headers
+      {}
     end
 
     def build_websocket_url