Add async-ssl-system-executor http client example

This example websocket client application uses the `system_executor` to show
how to use it with the I/O objects in ASIO and Beast.

Signed-off-by: Damian Jarek <damian.jarek93@gmail.com>

example/websocket/client/Jamfile

@@ -13,5 +13,6 @@ build-project sync ;
 
 # SSL
 build-project async-ssl ;
+build-project async-ssl-system-executor ;
 build-project coro-ssl ;
 build-project sync-ssl ;