v1.1.0: SSE disconnect fix

As reported in #16, SSEs will disconnect after a long period of time, or more particularly when client drops out from a network and does not automatically reconnect.

Two workarounds are applied:

1. Added listener to reconnect when stream ends
2. Added a keepalive interval to force reconnects every 5 minutes – this should ensure SSEs remain connected even if above stream end event does not fire