Added catchers for HTTP non-success status codes.
Make explicit that this predicate is private and different from the public predicate in URI_EXT.
ADDED: Images are now shown in the HTML generation for RDF terms.
JSON-2-RDF now asserts images using the new RDF image module.
Extended the way in which nested directories can be created: allow input for the form `Root(ListOfSubDirs)`.
Added is_image_file/1 for checking whether something is an image file based on extension.
Improves the way in which images are saved locally:
  1. Use the current project's data subdirectory.
  2. Create subdirectory path reflecting the URL, i.e. `Scheme/Authoirity/Path`.
Added RDF image assertions, where we can retrieve images for RDF terms that denote images by storing them locally.
The default number of retries upon a failed HTTP open is now `inf`...
Use typecheck module i.o. custom typecheck predicate.
Do not retry upon receiving 403 status.
Allow multiple CKAN sites to be loaded simultateously.
Changed format/1 option into graph/1 option.
small
Allow any HTTPS content to be retrieved.
Add URI typecheck as a mnemonic for IRI.
Small fixes to Doyle TMS assertions in RDF.
Fixed semideterminism for user properties.
Documented options for materialization.
Small fixes for TMS GraphViz export and other maintenance stuff.