Make conversion from IRI to DatatypeIDView public (#419)

Author: liss-h

src/rdf4cpp/IRI.hpp

@@ -17,14 +17,17 @@ struct IRI : Node {
      * it does not exist already.
      */
     IRI(datatypes::registry::DatatypeIDView id, storage::DynNodeStoragePtr node_storage) noexcept;
-    
+
+public:
     /**
      * Constructs the corresponding datatype id for this iri. Return value can be safely used to
      * index the registry and yields the correct result.
      */
-    explicit operator datatypes::registry::DatatypeIDView() const noexcept;
+    operator datatypes::registry::DatatypeIDView() const noexcept;
 
-public:
+    /**
+     * Constructs an IRI from a node backend handle
+     */
     explicit IRI(storage::identifier::NodeBackendHandle handle) noexcept;
 
     /**