If there are multiple language blocks on a page, we set the
onload on the last one to load all highlighting at once.
If the last language block has an error, the onload would
never fire and thus all blocks would not be highlighted.
The simplest resolution is to fire the callback regardless. We've
already loaded everything so running the callback is not causing any
performance hit which is relevant I think.
This adds a "Reader" section of the site for admins who want to enable
it for their instance. That means visitors can go to /read and see who
has publicly shared their writing. They can also follow all public posts
via RSS by going to /read/feed/. Writers on an instance with this
`local_timeline` setting enabled can publish to the timeline by going
into their blog settings and choosing the "Public" visibility setting.
The `local_timeline` feature is disabled by default, as is the Public
setting on writer blogs. Enabling it adds a "Reader" navigation item and
enables the reader endpoints. This feature will also consume more
memory, as public posts are cached in memory for 10 minutes.
These changes include code ported over from Read.Write.as, and thus
include some experimental features like filtering public posts by tags
and authors. These features aren't well-tested or complete.
Closes T554
