To generate HTML, you will need to get Rust, since it provides rustdoc that
does the job.
To generate spec.html:
make spec.html
Aside from spec.html you will want to include rust.css to get a nice
formatting of the spec.
Alternatively, you can generate just a body part of the webpage using Pandoc:
make spec-pandoc.html
If you want to contribute, don't forget to make sure that text formatting is correct by running:
make format
git diff