fixes hakimel/reveal.js#3231

[Markdown plugin] add line number offset for code sections to markdown

Correctly strip leading white-space from markdown

* Fix overlap in overview when config.disableLayout === true

* run gulp js
after commit 9193e5cd5d6d1aa234803b753c6d032b801a8221

---------

Co-authored-by: Hakim El Hattab <hakim.elhattab@gmail.com>

add sortFragmentsOnSync option, makes it possible to avoid unwanted sorting in editing environments like slides.com

Fixes https://github.com/hakimel/reveal.js/issues/3315

If the markdown contains something that is indented by more that the
`leadingTabs`/`leadingWs` then extra white space is incorrectly removed.
ie the following example:

```
    <section data-markdown>
    some text
       indented text
          more indented text
    </section>
```

would result in the following markdown:

```
some text
   indented text
  more indented text
```

We can work around this problem by using a function to generate the
replace value.

Fixes typos

Missing lang attribute

GitHub Workflows security hardening

Gulp livereload: include subfolders to watch for changes in html and md

Add theme 'dracula'