libXML now returnes info why XML is not valid (#218)

Co-authored-by: Adam Bem <adam.bem@zoho.eu>
Reviewed-on: #218
Reviewed-by: Mikolaj Widla <widlam@noreply.example.com>

Backend-libXML/Parser.py

@@ -77,10 +77,12 @@ def xsd(source: str, xsd: str) -> bool:
     document_input = BytesIO(source.encode("utf-8"))
     xml = etree.parse(document_input).getroot()
     
-    if xml_schema.validate(xml):
-        return "XML is valid."
-    else:
-        return "XML is NOT valid."
+    try:
+        xml_schema.assertValid(xml)
+        return "XML is valid"
+    except etree.DocumentInvalid as e:
+        return str(e)
+
     
     
 def xslt(source: str, xslt: str) -> str: