0.0.19

• support interval option in ping api, and pingInterval option in ews constructor.
• change minimal ping interval from 60s to 20s.

0.0.18

• watch for Connection errors so caller can handle those errors.

0.0.17

• prevent calling close and send without _ws
• make close-handler work only if event source = _ws
• use on instead of addEventListener for offline event

0.0.16

• due to untrustable close event, we move close event handler to a standalone function, and call it from both close and offline event.

0.0.15

• fire offline event when offline event received from window.
• upgrade dependencies

0.0.14

• support ping function, which send ping message to server every 60s by default if page is visible
• fix bug: status() should query status from _src if this is a scoped ws.

0.0.13

• pass op parameter from middleware submit action to access function for fine-grained access control

0.0.12

• fix bug: ws refresh causes ews losing event handlers.

0.0.11

• fix bug: pipe create new ews which depends on source ws, however source ws may update, may not ready yet,
  lead to unusable piped ews. additional tracing from root ews is added to update the whole ews pipe tree.
• upgrade dependencies

0.0.10

• wrap lderror in sharedb error format so we can't decode it back to a lderror object in client side.