Please add Auto complete feature ,like VSCode + Rust extension.

[ghost]

Hello, would you please add auto complete feature, like we coding with VSCode + Rust extension.

That would be help if we want really quick and test the feature about Rust.

We only need a browser, and visit https://play.rust-lang.org

Then it works, we need auto complete, to reminder us how to use rust library, functions.

[shepmaster]

Duplicate of #357