Still updating the architecture for loading VoID datasets and debugging tools surrounding that.

* [ANSI_EXT,SC] Simplified the implementation of ansi_format/4.
* [RDF_STATISTICS,EXT] Changed several predicates to be in agreement with the VoID specification a bit more.
* [THREAD_EXT,NEW] Added forall_thread/2 for creating multiple threads that run some consequent goal, based on the instantiations for some antecedent goal, and then joining those threads once they are all done.
* [VOID,SC] Use of THREAD_EXT to make the code more compact. Updated debugging statements and updated some old-fashioned API calls (to RDF_SERIAL).
* [WEB_MESSAGE,DEB] Also write debug messages to the terminal when they are sent to the Web front-end. Use ANSI_EXT for coloring.
1. I no longer want to run experiments on data files directly, but on (temporary) copies of that data. Therefore, some architecture is needed for shoving files around.
2. Various fixes while loading lots of data and making all kinds of assertions/updates.

* [DIR_EXT,NEW] Added predicates for creating and disassembling directories: append_directories/3, directory_to_subdirectories/2, subdirectories_to_directory/2.
* [DIR_EXT,NEW] Added predicates for safely deleting and copying directories (and their recursive contents): safe_copy_directory/2, safe_delete_directory/1, safe_delete_directory_contents/1.
* [DIR_EXT,NEW] Added predicates for copying directory structures to the personal directory of a project, in order to run experiments on data without affecting the original files and folders: experiment_directory/1, safe_copy_experiment_data/2.
* [DIR_EXT,SC] create_directory/1 now reuses directory_to_subdirectories/2.
* [DIR_EXT,DEB] Added debug messages.
* [FILE_EXT,DEB] Added debug messages.
* [RDF_BUILD,SC] Removed the value parameter from rdf_retractall_datatype.
* [RDF_BUILD,SC] Reimplemented rdf_overwrite_datatype/5.
* [THREAD_EXT,NEW] Added forall_thread_end/1, a method that can be used as the value of the at_exit/1 option.
* [THREAD_EXT,EXT] Use the SHA1 hash of the goal that is called in the thread as the alias of that thread.
* [VOID,FIX] Reverted to not using THREAD_EXT for repetitive thear calling. The alias cannot be passed through to the debug statement in at_exit/1... @tbd
* [XSD,FIX] Added many cuts for determinism.
* [XSD,DEB] Added debug messages in case a mapping is not found for the given datatype.
* [XSD_DATETIME,FIX] Wrong argument (code i.o. integer) given in yearFrag//1.