Queued events are ignored when flushing client

[ramosbugs]

The client flush method is implemented in terms of stopping and restarting the Transmission:

libhoney-rust/src/client.rs

Lines 122 to 133 in 2f7cdc8

	/// flush closes and reopens the Transmission, ensuring events are sent without
	/// waiting on the batch to be sent asyncronously. Generally, it is more efficient to
	/// rely on asyncronous batches than to call Flush, but certain scenarios may require
	/// Flush if asynchronous sends are not guaranteed to run (i.e. running in AWS Lambda)
	/// Flush is not thread safe - use it only when you are sure that no other parts of
	/// your program are calling Send
	pub fn flush(&mut self) -> Result<()> {
	info!("flushing libhoney client");
	self.transmission.stop()?;
	self.transmission.start();
	Ok(())
	}

Unfortunately, the stop event causes a break that breaks out of the loop and doesn't send any of the queued events:

libhoney-rust/src/transmission.rs

Lines 212 to 215 in 62d6da9

	if event.fields.contains_key("internal_stop_event") {
	info!("got 'internal_stop_event' event");
	break;
	}

I think the code should probably jump to this line instead of breaking out of the loop:

libhoney-rust/src/transmission.rs

Line 238 in 62d6da9

let mut batches_sent = Vec::new();