Submodules to bring other C4DC content into the site

This adds the submodules of the code of conduct repo and the guides repo. It also adds a script to allow those `.md` files to be inserted into a page using the `{% markdown your-file.md %}` tag. This is all used to make `codeofconduct.html` and include that directly on the site. It theoretically should work automatically, but I haven't tested it on a live gh-pages branch. Perhaps I'll make a temporary repo to do that.

If this works, we can also store the projects data as YAML instead of JSON and use Jekyll to build the projects page instead of Javascript. I don't know if that's good or not, but it's possible.