block.super doesn't work with pages

Using cryogen-core 0.3.1, I'd like to create a new page that overrides the default template's content block, inserting the original via `{{ block.super }}` (info in Selmer README). Instead I get the page template rendered with no values populated.

The project was freshly created using the default `page.html` template. I added a `page-premium.html` template with an extends block:

```
{% extends "/html/page.html" %}

{% block content %}

a
{{ block.super }}
b

{% endblock %}
```

And the page `premium.md`:

```
{:title "Premium"
:layout :page-premium}

Premo.
```

What I see is this:


And I'd expect to see "Premo." on the page between a and b.