Investigate the level of effort for adding support for an "LFE eval service" in mdbook

[oubiwann]

https://rust-lang.github.io/mdBook/format/mdbook.html#inserting-runnable-rust-files

I don't think we'd need to recompile mdbook; we might just be able to:

1. reuse {{#playground file.rs}} and
2. maintain a modified book.js that calls the LFE service instead of the Rust playground

Need to look at the details of how mdbook reads the results:

• https://github.com/rust-lang/mdBook/blob/master/src/renderer/html_handlebars/hbs_renderer.rs
• https://github.com/rust-lang/mdBook/blob/master/tests/rendered_output.rs

Questions:

• Does mdbook do any file extension checks? Iow, will {{#playground file.lfe}} work?