IDE support

When creating a new module for IDE support, consider to:
- [ ] Convert the semantics error (or the whole [pest::error][]) to [codespan][] to have error reporting similar to Rust (pest error reporting is not flexible)
- [ ] and automatically have support for [LSP][] (via [codespan-lsp][] when it's stable).

[pest::error]: https://docs.rs/pest/2.1.1/pest/error/struct.Error.html
[codespan]: https://github.com/brendanzab/codespan
[LSP]: https://microsoft.github.io/language-server-protocol
[codespan-lsp]: https://crates.io/crates/codespan-lsp

References:
- [Writing debugger and language extension for VSCode](https://www.codemag.com/article/1809051/Writing-Your-Own-Debugger-and-Language-Extensions-with-Visual-Studio-Code)