exerciser

This is an mdBook renderer to generate templates for exercises from the Markdown source. Given a Markdown file example.md with one or more sections like:

<!-- File src/main.rs -->

```rust,compile_fail
{{#include example/src/main.rs:main}}

fn some_more_code() {
    // TODO: Write some Rust code here.
}
```

and mdbook configuration in book.toml like:

[output.exerciser]
output-directory = "comprehensive-rust-exercises"

It will create a file book/exerciser/comprehensive-rust-exercises/example/src/main.rs with the appropriate contents.