Add callback for handling internal links

[mihai-wolfpack]

No description provided.

[stevenzeck]

I think this is fine for now. I wanted to see what happens if it can't find the file that matches the URL of the internal link. In that case, it logs an error and the reader simply goes to the first resource of the book.

[mickael-menu]

Ha, probably something to handle in go() to abort (and return false) if the link.href can't be found in the readingOrder. It's not directly related to this PR though, so not a blocking issue for the review. I guess the same would happen if a table of contents has a broken link.

[mickael-menu]

@mihai-wolfpack @stevenzeck

I pushed a fix where we lost the HTML anchor in internal links (e.g. chapter01.xhtml#section-a) but I'd like for you to review before I merge this PR. Thanks!

[mihai-wolfpack]

@mickael-menu @stevenzeck

Everything looks good to me! 👍