WebSocketSessionMan now implements DownloadEventListener and is added
to Notifier. It becomes member variable of DownloadEngine. The event
constant for download event is defined in aria2.h so that we can add
event callback API later.
To enable RPC over SSL/TLS, specify server certificate and private key
using --rpc-certificate and --rpc-private-key options and enable
--rpc-secure option. After the encryption is enabled, use https and
wss scheme to access RPC server.
Tatsuhiro Tsujikawa