2014-08-02-foo.md

Hi there

_config.yml

defaults:
  -
    scope:
      path: ""
    values:
      layout: "page"
  -
    scope:
      path: "_posts"
    values:
      layout: "post"

foo.html

<!-- page layout -->
<p>Hi there</p>

page.html

<!-- page layout -->
{{ content }}

post.html

<!-- post layout -->
{{ content }}