Fix layout to deal with missing title.
Add blog layout.
Add layout for article summaries.
Add a helper function to get post summaries.
Add the blog index and a sample post.
Add rules for blog posts.
Add another sample post.
Add layout for blog articles.
Add title attribute to blog index.

This is a duplicate of the
blog name attribute in nanoc.yaml.
Unfortunately, it is not possible to use ERB
in the front matter, so we cannot use @config[:blog][:name]
here.
Allow posts to override contact_url attribute.
Modify front matter of sample posts.

All attributes are optional (if the article does
not have a `title` attribute, however, no title
will be printed in the output). If `kind` is omitted,
it is set to `article` during the pre-processing phase.
If `created_at´ is omitted, then it is set to the
current date on preprocessing. If `excerpt` is
omitted, but a `<!-- more -->` separator is present
in the post (see Simple Post), then that will be
used to delimit the summary. The default author and
contact URL defined in nanoc.yaml can be overridden,
too, on a per-post base.
Cosmetic changes.
Make partials for tag lists and “posted on” snippets.
Add helper functions for generating tag pages.

See also: http://chickenboot.com/2013/05/24/zurb-foundation-with-nanoc-part-4/
Add rules to compile and route tag pages.
Add layout to generate the page for a given tag.
Add tag lists (with counts) to the sidebar.
Put blog extensions in a module, and include it.
Print updated_at if defined.
Add support for Atom feed.