Use underscore naming convention for "non-pages"
Required assets (`_assets/**` and `_search.json`) are included manually in `_config.yml`. Using this naming convention, "non-pages" can easily be filtered out when looping through `site.pages`.

The fact that `_`'ered pages appear before normal pages also allows valid JSON generation as one can rely on `forloop.last` when inserting object separators.

Lastly, this is the naming convention that will be used when Sass support is added to Jekyll. The future, today!