Handle multiple websocket connections
Handle multiple websocket connections

Sometimes I (accidentally or deliberately) have more than one browser
window or tab open to my app, and in that case I would like all of
them to refresh when I change the code.

The old behaviour is that just one client, the last to connect to the
websocket server, would refresh when the `reloadServer.reload()` method
is called.

Note that this only changes the behaviour when the `reloadServer.reload()`
function is used: it would always behave correctly if the clients are signalled
by stopping the server.

This PR changes (an undocumented property of) the public API, in that the
`.connection` object is replaced by a `.connections` object. HOWEVER, this
change will not break any existing code, for the simple reason that previously
the `.connection` object was always undefined! The code was returning it before
it had been assigned: it was assigned in the handler for the wss "connection" event.

jprichardson/reload,jprichardson/reload,alallier/reload