Figure out a way to make empty front matter optional

[mojavelinux]

Currently, it's necessary to add an empty front matter block at the top of the page, even if that block is empty (and all front matter is defined using AsciiDoc attributes). Otherwise, the AsciiDoc document is not recognized as a page. This empty front matter block makes the AsciiDoc document non-conforming by default (unless the skip-front-matter attribute is passed to the processor) and adds an extra step when migrating an AsciiDoc document to a Jekyll site.

Figure out a way, perhaps using Jekyll hooks, to make this empty front matter optional.

[mojavelinux]

The method we need to override is Jekyll::Utils.has_yaml_header?. I think we should always return true for AsciiDoc files. We may want to put this behavior behind a switch in the configuration.