add release_queue() to Client and Eventloop

[andresv]

This PR adds Client::release_queue() and Eventloop::release_queue(). Those can be called before dropping Client and Eventloop to get back original producer and consumer that can be given back to BBQueue after that. Useful when you want to reinit everything from scratch.

let prod = mqtt_client.release_queue().unwrap();
let cons = mqtt_eventloop.release_queue().unwrap();
mqtt_queue.try_release_framed(prod, cons);

drop(mqtt_client);
drop(mqtt_eventloop);

[codecov-commenter]

Codecov Report

Base: 39.16% // Head: 39.21% // Increases project coverage by +0.05% :tada:

Coverage data is based on head (fcc513e) compared to base (3f175ec). Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #53 +/- ## ========================================== + Coverage 39.16% 39.21% +0.05% ========================================== Files 13 13 Lines 1177 1178 +1 Branches 338 337 -1 ========================================== + Hits 461 462 +1 Misses 568 568 Partials 148 148 ``` | [Impacted Files](https://codecov.io/gh/BlackbirdHQ/mqttrust/pull/53?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=BlackbirdHQ) | Coverage Δ | | |---|---|---| | [mqttrust/src/lib.rs](https://codecov.io/gh/BlackbirdHQ/mqttrust/pull/53/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=BlackbirdHQ#diff-bXF0dHJ1c3Qvc3JjL2xpYi5ycw==) | `100.00% <ø> (ø)` | | | [mqttrust\_core/src/lib.rs](https://codecov.io/gh/BlackbirdHQ/mqttrust/pull/53/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=BlackbirdHQ#diff-bXF0dHJ1c3RfY29yZS9zcmMvbGliLnJz) | `32.25% <ø> (ø)` | | | [mqttrust\_core/src/eventloop.rs](https://codecov.io/gh/BlackbirdHQ/mqttrust/pull/53/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=BlackbirdHQ#diff-bXF0dHJ1c3RfY29yZS9zcmMvZXZlbnRsb29wLnJz) | `35.98% <100.00%> (+0.30%)` | :arrow_up: | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=BlackbirdHQ). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=BlackbirdHQ)

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[andresv]

CI errors seems to be unrelated to my change.

[andresv]

Wanna merge?