Allow Jinja2 tags inside Markdown body

[jeremydw]

No description provided.

[jeremydw]

This isn't supported by default, but rather explicitly. You can use {{doc.html|render}} to render the document's body as a Jinja2 template. Note that the template currently inherits the template context of the scope it's in. This decision was done to make using template tags inside Markdown more frictionless. It's also consistent with how Jekyll works.

Minor documentation: http://preview.growsdk.org/docs/documents/#html-body