Turning reveal-hugo theme into a hugo module

[deining]

This PR turns the reveal-hugo theme into a hugo module. With gitand go installed, preview of the userguide theme is now as easy as:

git clone https://github,com/dzello/reveal-hugo
cd exampleSIte
hugo server

The successful netlify preview for this PR proves that this approach is valid.

Copying/cloning the theme in the themes folder is still possible of course.

I amended instructions on how to use theme as hugo module with new and existing sites to README.md. Also, I added instructions on how to update the theme when used as hugo module (via hugo mod get -u github,com/dzello/reveal-hugo).

I hope you like the idea of using reveal-hugo as hugo module.

[joshed-io]

Thanks @deining! I'll set aside a few minutes to review this week. I need to learn more about hugo modules but it seems like a sensible approach.

[davidovich]

This change also suggests that the repository starts tagging releases as valid semantic versions with the v prefix (i.e. v0.1.0). Although tagging is not strictly necessary to enable hugo modules, it makes it clearer for consumers when a new feature or bug fix is introduced in the theme.

[deining]

Thanks @deining! (...) I need to learn more about hugo modules but it seems like a sensible approach.

I updated my PR so that we now use HEAD of repo as module's version. Any chance to see that reviewed soon? Thanks in advance.

[deining]

Thanks for your review comments, which are addressed now. Looking forward to see this PR merged soon.

[joshed-io]

@deining @davidovich Thank you! 🙏