* Add search with elasticlunr.js
This commit adds search functionality to mdBook, based on work done by @phaiax. The in-browser search code uses elasticlunr.js to execute the search, using an index generated at book build time by elasticlunr-rs.
* Add generator comment
Someone on Reddit was wondering how the rust book was generated and said they checked the source. Thought I'd put this here. Might be a good idea to have a little footer "made with mdBook", but this'll do for now.
* Remove search/editor file override behavior
* Use for loop for book iterator
* Improve HTML regex
* Fix search CORS in file URIs
* Use ammonia to sanitize HTML
* Filter html5ever log messages
* First version of preprocessor example, with quicli
It seems it's not worth it right now.
* Remove quicli, just to simplify everything
* Finish de-emphasise example
* Finish preprocessor example in book
* Rename preprocessor type
* Apply changes requested in review
* Update preprocessor docs with latest code
[skip CI]
