split-stream-by 0.0.0

This repo is for a rust crate that offers a `futures::Stream` extension
trait which allows for splitting a `Stream` into two streams using a
predicate function thats checked on each `Stream::Item`.

```rust
use split_stream_by::SplitStreamByExt;

let incoming_stream = futures::stream::iter([0,1,2,3,4,5]);
let (mut even_stream, mut odd_stream) = incoming_stream.split_by(|&n| n % 2 == 0);

tokio::spawn(async move {
	while let Some(even_number) = even_stream.next().await {
		println!("Even {}",even_number);
	}
});

while let Some(odd_number) = odd_stream.next().await {
	println!("Odd {}",odd_number);
}
```

A more advanced usage uses `split_by_map` which allows for extracting
values while splitting

```rust
use split_stream_by::{Either,SplitStreamByExt};

struct Request {
	//...
}

struct Response {
	//...
}

enum Message {
	Request(Request),
	Response(Response)
}

let incoming_stream = futures::stream::iter([
	Message::Request(Request {}),
	Message::Response(Response {}),
	Message::Response(Response {}),
]);
let (mut request_stream, mut response_stream) = incoming_stream.split_by_map(|item| match item {
	Message::Request(req) => Either::Left(req),
	Message::Response(res) => Either::Right(res),
});

tokio::spawn(async move {
	while let Some(request) = request_stream.next().await {
		// ...
	}
});

while let Some(response) = response_stream.next().await {
	// ...
}
```

In its current implementation, it only buffers up to one element in the
scenario where the stream that requests the next item is not the one
that matches the predicate. In the future, this might be changed to be
configurable using a const generic parameter