v0.16.5

• Minor API change in some to_json_string() methods (no config parameter needed)
• Added to_json_value() method alongside to_json_string() (returns serde_json::Value)
• Fix in JSON serialisation of DataValue:null
• Implemented to_json_string(), to_json_value() and text() for QueryResultItem
• Minor dependency upgrades
• Added extra_target_template parameter in WebAnnoConfig for web annotation serialisation. This adds an extra target during serialisation of web annotations that resolves the TextPositionSelectors to a single IRI/URI (according to the template).