These are included in the manifest so that hosts can discover them.  Having
them in the data file as well is redundant, and in some cases requires an
otherwise unnecessary import of the core spec.

Towards putting more here than just the project metadata, and is a bit cleaner
of a naming scheme anyway.

This caused weird syntax highlighting in the documentation.

This makes it feasible to merge the LV2 documentation into more broad
documentation in a meta-project.

This removes all the extra bundle content from the documentation output and
instead makes pages directly at the URI of specifications.  This way, links to
fragments in spec pages (which are often copy and pasted) are correct fragment
identifiers like <http://lv2plug.in/ns/lv2core#Plugin> instead of
<http://lv2plug.in/ns/lv2core/#Plugin>.