Generator does not support C++, Rust, Objective-C, PowerShell and others

Description

What is the status of C++, Rust, Objective-C, PowerShell and some other languages listed as supported in the current README.md but actually not supported by the currently latest Swagger Codegen JAR.

The current README.md says:

Currently, the following languages/frameworks are supported:
API clients: ActionScript, Ada, Apex, Bash, C# (.net 2.0, 3.5 or later), C++ (cpprest, Qt5, Tizen), Clojure, Dart, Elixir, Elm, Eiffel, Erlang, Go, Groovy, Haskell (http-client, Servant), Java (Jersey1.x, Jersey2.x, OkHttp, Retrofit1.x, Retrofit2.x, Feign, RestTemplate, RESTEasy, Vertx, Google API Client Library for Java, Rest-assured), Kotlin, Lua, Node.js (ES5, ES6, AngularJS with Google Closure Compiler annotations) Objective-C, Perl, PHP, PowerShell, Python, R, Ruby, Rust (rust, rust-server), Scala (akka, http4s, swagger-async-httpclient), Swift (2.x, 3.x, 4.x, 5.x), Typescript (Angular1.x, Angular2.x, Fetch, jQuery, Node)

Swagger-codegen version

3.0.26

Steps to reproduce

Related issues/PRs

java -jar .\swagger-codegen-cli-3.0.26.jar config-help -l cpprest
java -jar .\swagger-codegen-cli-3.0.26.jar config-help -l rust
java -jar .\swagger-codegen-cli-3.0.26.jar config-help -l objective-c
java -jar .\swagger-codegen-cli-3.0.26.jar config-help -l powershell