WIP: Correct readme index preprocessing

[duchainer]

Closes #1268

Uses commented regexes for matching inline and reference-style links.

https://github.com/badboy/mdbook-toc

https://docs.rs/pulldown-cmark/0.7.2/pulldown_cmark/

https://docs.rs/pulldown-cmark/0.7.2/pulldown_cmark/enum.LinkType.html
pulldown_cmark::LinkType - Rust
API documentation for the Rust LinkType enum in crate pulldown_cmark.

use pulldown_cmark::{Event, LinkType, Options, Parser};
fn main() {
    let md_input = r#"
# My title
[title]: #my-title

Hi im referencing [title] as well as a [reference][1] and [inline](./heelo.md)

[1]: ./Hai.md

    "#;

    let opts = Options::all();

    let parse = Parser::new_ext(md_input, opts);

    for elem in parse {
        println!("{:?}", elem);
    }
}```

[duchainer]

Waiting for the merge of link definition to complete this PR : pulldown-cmark/pulldown-cmark#423. Until then, this code is open to any edits as I'll comment before returning to this issue. Code away. ^^

[rustbot]

☔ The latest upstream changes (possibly #2681) made this pull request unmergeable. Please resolve the merge conflicts.