core: Keep refactoring, this time to prepare for generator sources. - Make a few APIs simpler. - Content pipelines create their own jobs, so that generator sources can keep aborting in `getContents`, but rely on their pipeline to generate pages for baking.

{% extends "section-page.html" %}

{% block header %}
<header class="documentation">
    <h1>{{ page.title }}</h1>
</header>
{% endblock %}