XSD schema validation
The schema validation mechanism is built in and performs dummy validation for the root <inishell_config> node, but the actual xsd file is not written yet. The INIshell logger gives a lot of info about invalid panel nodes, and the XML parser displays all errors as well. Still, the schema validation does just what is missing: check for unknown attributes etc, and it would be nice to have available for e. g. the person writing the SNOWPACK & Alpine3D XMLs.