Notify the delegate of events after updating our internal state

Should the delegate decide to inspect the given EventSource, its state should
be consistent. Otherwise, the following assertion would fail:

- (void)eventSourceDidClose:(TRVSEventSource *)eventSource {
    NSAssert(eventSource.isClosed, @"Event source should be closed");
}
Merge pull request #2 from travisjeffery/notify-delegate-last

Notify the delegate of events after updating our internal state