Major plugin refactor and cleanup.

Switched to POCO library for unified platform/library interface.
Deprecated the external module API. It was creating more problems than solving.
Removed most built-in libraries in favor of system libraries for easier maintenance.
Cleaned and secured code with help from static analyzers.

vendor/POCO/XML/include/Poco/SAX/DTDHandler.h

@@ -0,0 +1,86 @@
+//
+// DTDHandler.h
+//
+// Library: XML
+// Package: SAX
+// Module:  SAX
+//
+// SAX DTDHandler Interface.
+//
+// Copyright (c) 2004-2006, Applied Informatics Software Engineering GmbH.
+// and Contributors.
+//
+// SPDX-License-Identifier:	BSL-1.0
+//
+
+
+#ifndef SAX_DTDHandler_INCLUDED
+#define SAX_DTDHandler_INCLUDED
+
+
+#include "Poco/XML/XML.h"
+#include "Poco/XML/XMLString.h"
+
+
+namespace Poco {
+namespace XML {
+
+
+class XML_API DTDHandler
+	/// If a SAX application needs information about notations and unparsed entities, 
+	/// then the application implements this interface and registers an instance with the 
+	/// SAX parser using the parser's setDTDHandler method. The parser uses the instance 
+	/// to report notation and unparsed entity declarations to the application.
+	///
+	/// Note that this interface includes only those DTD events that the XML recommendation 
+	/// requires processors to report: notation and unparsed entity declarations.
+	///
+	/// The SAX parser may report these events in any order, regardless of the order in 
+	/// which the notations and unparsed entities were declared; however, all DTD events 
+	/// must be reported after the document handler's startDocument event, and before the first 
+	/// startElement event. (If the LexicalHandler is used, these events must also be reported before the endDTD event.)
+	/// 
+	/// It is up to the application to store the information for future use (perhaps in a hash table or 
+	/// object tree). If the application encounters attributes of type "NOTATION", "ENTITY", or "ENTITIES", 
+	/// it can use the information that it obtained through this interface to find the entity and/or notation
+	/// corresponding with the attribute value.
+{
+public:
+	virtual void notationDecl(const XMLString& name, const XMLString* publicId, const XMLString* systemId) = 0;
+		/// Receive notification of a notation declaration event.
+		/// 
+		/// It is up to the application to record the notation for later reference, 
+		/// if necessary; notations may appear as attribute values and in unparsed 
+		/// entity declarations, and are sometime used with processing instruction 
+		/// target names.
+		/// 
+		/// At least one of publicId and systemId must be non-null. If a system identifier 
+		/// is present, and it is a URL, the SAX parser must resolve it fully before passing 
+		/// it to the application through this event.
+		/// 
+		/// There is no guarantee that the notation declaration will be reported before any 
+		/// unparsed entities that use it.
+		///
+		/// Note that publicId and systemId maybe null, therefore we pass a pointer rather than a reference.
+		
+	virtual void unparsedEntityDecl(const XMLString& name, const XMLString* publicId, const XMLString& systemId, const XMLString& notationName) = 0;
+		/// Receive notification of an unparsed entity declaration event.
+		/// 
+		/// Note that the notation name corresponds to a notation reported by the 
+		/// notationDecl event. It is up to the application to record the entity for 
+		/// later reference, if necessary; unparsed entities may appear as attribute values.
+		/// 
+		/// If the system identifier is a URL, the parser must resolve it fully before 
+		/// passing it to the application.
+		/// 
+		/// Note that publicId maybe null, therefore we pass a pointer rather than a reference.
+
+protected:
+	virtual ~DTDHandler();
+};
+
+
+} } // namespace Poco::XML
+
+
+#endif // SAX_DTDHandler_INCLUDED