Following up in #147, this PR converts the theme into a hugo module and automatically pulls in bulma as dependency.

With this PR in place, setting up a new site based on shadocs can be done via:

hugo new site my-site
cd my-site
hugo mod init github.com/me/my-site
hugo mod get github.com/jgazeau/shadocs #optional
echo 'theme = "github.com/jgazeau/shadocs" >> config.toml
hugo server

With this PR applied, you can preview the exampleSite simply via hugo server (no bulma submodule checkout and themesDir=../.. needed any more).

Notes:

• deploy on netlify and other checks fail currently. This is to be expected since we have a chicken - egg problem here. Once this PR is merged, checkers should go green again
• if you follow this route, your future tags/releases should have the form v1.3.0 (note the leading v), since this conforms to go`s naming convention for go modules.
• if you want to continue to provide a zip-archive, you should issue hugo mod vendor at the command prompt. This creates a directory _vendor containing the theme module sources (incl. bulma dependency).
• Updating the theme is super easy now: hugo mod get -u github.com/jgazeau/[email protected]. That's it!
• Same for updating bulma within the theme itself: hugo mod get -u github.com/jhthms/[email protected]
• I did intentionally small commits, we can squash them into one when merging this PR.

I hope you like my PR. With this PR in place, we have the foundation to get some goodies added to your theme, I have something in mind here.

This PR closes #147.