The default is for hyphens to separate tokens in search terms: `gem-based` is equivalent to `gem based`.

This adds `search_tokenizer_separator` as a site configuation option, to support search for hyphenated words.

This commit makes the dark mode preview feel a little more interactive
and it also pulls some duplicated code into one file so that people like
me aren't stumped when they are looking at the wrong page!

If you exclude the last page in the site.html_pages through exclude_true you end up violating the assumption in the for loop that the last page won't have a trailing comma. This breaks the json data that is served to the front end.

I removed the forloop.last check and instead assign a temporary variable to check for the first non-excluded page, and then add the comma before the next non-excluded entry.

Because `page.title` (and `page.url`) is already escaped and page titles served by lunrjs do not need escaping, ampersands need to be unescaped to display properly in search results.

and mention `search_exclude`