Revealjs feature request: line number offset

[andrewpbray]

Version 4.2.0 of revealjs implemented a feature that allows you to specify the line number on which a code chunk will start. I don't see it as a must-have feature, but it'd be helpful when displaying more than one chunk of code from the same file.

Description of feature:
https://revealjs.com/code/#line-number-offset-4.2.0

Changelog:
https://github.com/hakimel/reveal.js/releases/tag/4.2.0

[mcanouil]

Closing in favour of #1454