Convert all the links in the generated print.html for linking inside the book into URL fragment form

[HollowMan6]

I'm requesting for a feature that convert all the links in the generated print.html that link to another html page inside the "book" into the URL fragment form, so that once a user click that link, they will be guided to the corresponding spot instead of another html page (This should be obvious as print.html includes all the generated book content, the current behavior is some kind of weird).

For one example of the mdBook Documentation (Notice URL change):

• Current Behavior:
  

• Expected Behavior:
  

For use case: #88 (comment)

[HollowMan6]

Well, I just noticed that developers have already noticed this issue: https://github.com/rust-lang/mdBook/blob/v0.4.15/src/utils/mod.rs#L73-L74 , it may be quite difficult, but still I hope someone can resolve this.