docs: Add feature info and increment API version

docs: Add feature info and increment API version

The following patch will add the generated schema files as they are very
large.

* Increment the API version from v1.3 to v1.4.
* Update schema documentation to reflect the version change.
* Add blurb documenting the "Depends-on" tag to the usage overview.

Signed-off-by: Adam Hassick <ahassick@iol.unh.edu>
Acked-by: Aaron Conole <aconole@redhat.com>
[stephenfin: Tweak docs]
Signed-off-by: Stephen Finucane <stephen@that.guru>