KEEPALIVED support

[xmrig]

Response when miner send keepalived:

{
  "error": [
    -3,
    "Method name parsing failed. You *must* use format <service name>.<method name>, e.g. 'example.ping'",
    "Traceback: <class 'stratum.custom_exceptions.MethodNotFoundException'>: Method name parsing failed. You *must* use format <service name>.<method name>, e.g. 'example.ping'\n/usr/local/lib/python2.7/dist-packages/twisted/internet/posixbase.py:597:_doReadOrWrite\n/usr/local/lib/python2.7/dist-packages/twisted/internet/tcp.py:208:doRead\n/usr/local/lib/python2.7/dist-packages/twisted/internet/tcp.py:214:_dataReceived\n/root/xmr-proxy/stratum/protocol.py:194:dataReceived\n--- <exception caught here> ---\n/root/xmr-proxy/stratum/protocol.py:240:lineReceived\n/root/xmr-proxy/stratum/services.py:13:_handle_event\n/root/xmr-proxy/stratum/services.py:66:call\n"
  ],
  "id": 1,
  "result": null
}

[Atrides]

Fixed