They will be described in the release notes, but gist:

Added:
- `DeliverSubject()` option to configure the deliver subject of a JetStream consumer created by the `js.Subscribe()` call (and variants)
- `BindDeliverSubject()` option to subscribe directly to a JetStream consumer deliver subject (bypassing any lookup or JetStream consumer creation)
- Fields `DeliverGroup` in `ConsumerConfig`, `PushBound` in `ConsumerInfo`. They help making prevent incorrect subscriptions to JetStream consumers
- Field `Last` in `SequencePair`

Changed:
- With a `PullSubscription`, calling `NextMsg()` or `NextMsgWithContext()` will now return `ErrTypeSubscription`. You must use the `Fetch()` API
- If the library created internally a JetStream consumer, the consumer will be deleted on `Unsubscribe()` or when the `Drain()` completes
- Fail multiple instances of a subscription on the same durable push consumer (only one active at a time). Also, consumers now have the concept of `DeliverGroup`, which is the queue group name they are created for. Only queue member from the same group can attach to this consumer, and a non queue subscription cannot attach to it. Note that this requires server v2.3.5
- Attempting to create a queue subscription with a consumer configuration that has idle heartbeats and/or flow control will now result in an error

Fixed:
- Possible lock inversion
- JetStream consumers could be incorrectly deleted on subscription's `Unsubscribe()`

Resolves #785
Resolves #776
Resolves #775
Resolves #748
Resolves #747

Signed-off-by: Ivan Kozlovic <ivan@synadia.com>

Signed-off-by: Ivan Kozlovic <ivan@synadia.com>

Signed-off-by: Ivan Kozlovic <ivan@synadia.com>

As discussed with Matthias who came up with the idea, this is
better because then we make use of the provided subject. Otherwise
it was looking weird to have something which meaning was:
```
js.SubscribeSync("ignored", nats.BindDeliverSubject("p.d4"))
```
Instead you would now have:
```
sub, err = js.SubscribeSync("p.d4", nats.SubjectIsDelivery())
```

Signed-off-by: Ivan Kozlovic <ivan@synadia.com>