Custom headers client

[mrbluecoat]

Unfortunately, browsers don't support setting this header for an EventSource object, so by default the last message id is set either from the "Last-Event-Id" header or the last_event_id url query string argument.
This behavior can be configured via the nchan_subscriber_last_message_id config.
A message's content-type will not be received by an EventSource subscriber, as the protocol makes no provisions for this metadata

Perhaps include an example with https://github.com/mpetazzoni/sse.js that does support custom headers