Update the default archetype to specify all relevant frontmatter fields.
Updated the bigimg and comments features to handle "unset" or "null"
values in the frontmatter and default appropriately. Also updated the
bigimg sample to explain both the default and "flow" YAML syntax.
Add support for big title images
(e6cb0a4f54).
Several bugfixes including pygment_highlights.css dependency, Index page
alignment/containers, and Index page site title. Also renamed
description to subtitle, in line with the original theme.