v3.4.1

This is a minor bug-fix and performance enhancement release.

ENHANCEMENT: Update the asynchronous pull query engine to use indexed lookups for joins.
FIX: Constructors for SPARQL update commands now validate inputs to guard against null values for required parameters. Documentation has been updated for the affected classes.
FIX: Fixed the logic for determining the base URI specified by custom RDF handlers when parsing. Thanks to @rorlic for the report. (#758)