Include code examples from files

[catamorphism]

Some code examples -- for example, the .wit example in https://component-model.bytecodealliance.org/language-support.html#language-agnostic-tooling -- are in files that exist in the repo in the examples directory. It would be nice to include these files directly in the Markdown rather than copy/pasting. As far as I can tell, pure Markdown and mdbook don't support this functionality (comment if I'm wrong!), but an extension, mdbook-utils, does support it. See first comment.

[vados-cosmonic]

Hey @catamorphism it looks like I was too late to respond, but with regards to including files we do support that currently and do it in the Rust guide for example.

[catamorphism]

@vados-cosmonic great, I see that now! I'll use that in #282 and will leave this issue open because there are other examples that could be included that are currently copy/pasted (e.g. the C/C++ section).