… of semantic ones (nicolas-grekas)This PR was merged into the 4.2-dev branch.Discussion----------[Messenger] remove classifying sub-namespaces in favor of semantic ones| Q             | A| ------------- | ---| Branch?       | 4.2| Bug fix?      | no| New feature?  | no| BC breaks?    | no| Deprecations? | no| Tests pass?   | yes| Fixed tickets | -| License       | MIT| Doc PR        | -While working on the component, I found it hard to discover the meaning of the `Asynchronous` and `Enhancers` sub-namespaces. Now that I know the component better, I understand they're only classifying namespaces with no specific technical semantics.I'd like to remove them to make the component easier to discover.This PR introduces a few new semantic sub-namespaces instead.From the changelog:  * Classes in the `Middleware\Enhancers` sub-namespace have been moved to the `Middleware` one * Classes in the `Asynchronous\Routing` sub-namespace have been moved to the `Transport\Sender\Locator` sub-namespace * The `Asynchronous/Middleware/SendMessageMiddleware` class has been moved to the `Middleware` namespace * `SenderInterface` and `ChainSender` classes have been moved to the `Transport\Sender` sub-namespace * `ReceiverInterface` and its implementations have been moved to the `Transport\Receiver` sub-namespaceCommits-------16afb5e [Messenger] remove classifying sub-namespaces in favor of semantic ones