[Rust] Enhancements to Rust server generator

Description

• rust2 is not a very informative name (renamed to rust-server via https://github.com/swagger-api/swagger-codegen/pull/6747)
• Currently uses hyper 0.10 - work underway to upgrade to hyper 0.11 (which adds full async support)
• Documentation on how to use the generated code in a Rust project is lacking
• Consolidate the client generator with rust generator (rust-server generates both server and client code)
• Add a means of testing rust-server's XML support back in (in a way that doesn't break everything else!). I believe other generators already do this, so it should not be over-hard.
• The rust-server sample was generated from the pre-reversion petstore yaml. It should be re-generated from the current petstore yaml.

Swagger-codegen version

Latest master

Related issues/PRs

https://github.com/swagger-api/swagger-codegen/pull/6613

Suggest a fix/enhancement

If anyone wants to work on these tasks, please reply to let us know.