Subscription (reactive-streams 1.0.3 API)

```
public interface Subscription
```
A Subscription represents a one-to-one lifecycle of a Subscriber subscribing to a Publisher.
It can only be used once by a single Subscriber.
It is used to both signal desire for data and cancel demand (and allow resource cleanup).

Method Summary

All Methods Instance Methods Abstract Methods
Modifier and Type	Method	Description
`void`	`cancel()`	Request the `Publisher` to stop sending data and clean up resources.
`void`	`request(long n)`	No events will be sent by a `Publisher` until demand is signaled via this method.

- Method Detail
  - request
```
void request(long n)
```
    No events will be sent by a Publisher until demand is signaled via this method.
    It can be called however often and whenever needed—but if the outstanding cumulative demand ever becomes Long.MAX_VALUE or more, it may be treated by the Publisher as "effectively unbounded".
    Whatever has been requested can be sent by the Publisher so only signal demand for what can be safely handled.
    A Publisher can send less than is requested if the stream ends but then must emit either Subscriber.onError(Throwable) or Subscriber.onComplete().
    
    Parameters:
    
    n - the strictly positive number of elements to requests to the upstream Publisher
  - cancel
```
void cancel()
```
    Request the Publisher to stop sending data and clean up resources.
    Data may still be sent to meet previously signalled demand after calling cancel.