This adds the ability to redirect URLs with `#` fragments. This is
useful when section headers get renamed or moved to other pages.
This works both for deleted pages and existing pages.
The implementation requires the use of JavaScript in order to manipulate
the location. (Ideally this would be handled on the server side.)
This also makes it so that deleted page redirects preserve the fragment
ID. Previously if you had a deleted page redirect, and the user went to
something like `page.html#foo`, it would redirect to `bar.html` without
the fragment. I think preserving the fragment is probably a better
behavior. If the new page doesn't have the fragment ID, then no harm is
really done. This is technically an open redirect, but I don't think
that there is too much danger with preserving a fragment ID?
The reason the ACE editor was failing to load the rust syntax
highlighting is because the syntax highlighting was being created
*after* the editor was created. If the editor is created first, then ACE
tries to load `ace/mode/rust`. Since it isn't already defined, it tried
to compute the URL and load it manually. However, since the URLs now
have a hash in it (via https://github.com/rust-lang/mdBook/pull/1368),
it was unable to load.
The solution here is to make sure `ace/mode/rust` is defined before
creating the editors. Then ACE knows that it can just load the module
directly instead of trying to fetch it from the server.
Fixes https://github.com/rust-lang/mdBook/issues/2700
This fixes a problem where the search was not displaying in
sub-directories. The problem was that `searcher.js` only exists in one
place, and was loading `searchindex.json` with a relative path. However,
when loading from a subdirectory, it needs the appropriate `..` to reach
the root of the book.
