* Per section/subsection feeds
* Added `generate_feed` variable to section front matter.
* Generate atom/rss feeds for sections/subsections that have the
`generate_feed` variable set to true (false by default); this works
independent of the `generate_feed` variable in the root `config.toml`
file, however, the name (and template) of the feed file for each section
is the same as `feed_filename` in `config.toml`, just located in the
root of each section.
* Slightly edited `atom.xml` and `rss.xml` so that they include the
section title (if any), and the url of a section, if it's a section
feed.
* Section feeds: tests
* Changed a couple of sections' front matter in order to generate feeds
for them for the test.
* Changed the can_build_feed test in site package to can_build_feeds and
included some assertions to make sure that section feeds are generated
when requested.
* Section feeds: documentation
* Added information about the section front matter variable
`generate_feed` in the section content page.
* Added information about section feeds in the feeds template page.
* Section feeds fix: use section.path for feed path
