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/Encodings/include/Poco/Encodings.h

@@ -0,0 +1,73 @@
+//
+// Encodings.h
+//
+// Library: Encodings
+// Package: Encodings
+// Module:  Encodings
+//
+// Basic definitions for the Poco Encodings library.
+// This file must be the first file included by every other Encodings
+// header file.
+//
+// Copyright (c) 2018, Applied Informatics Software Engineering GmbH.
+// and Contributors.
+//
+// SPDX-License-Identifier:	BSL-1.0
+//
+
+
+#ifndef Encodings_Encodings_INCLUDED
+#define Encodings_Encodings_INCLUDED
+
+
+#include "Poco/Foundation.h"
+
+
+//
+// The following block is the standard way of creating macros which make exporting
+// from a DLL simpler. All files within this DLL are compiled with the Encodings_EXPORTS
+// symbol defined on the command line. this symbol should not be defined on any project
+// that uses this DLL. This way any other project whose source files include this file see
+// Encodings_API functions as being imported from a DLL, whereas this DLL sees symbols
+// defined with this macro as being exported.
+//
+#if defined(_WIN32) && defined(POCO_DLL)
+	#if defined(Encodings_EXPORTS)
+		#define Encodings_API __declspec(dllexport)
+	#else
+		#define Encodings_API __declspec(dllimport)
+	#endif
+#endif
+
+
+#if !defined(Encodings_API)
+	#if !defined(POCO_NO_GCC_API_ATTRIBUTE) && defined (__GNUC__) && (__GNUC__ >= 4)
+		#define Encodings_API __attribute__ ((visibility ("default")))
+	#else
+		#define Encodings_API
+	#endif
+#endif
+
+
+//
+// Automatically link Encodings library.
+//
+#if defined(_MSC_VER)
+	#if !defined(POCO_NO_AUTOMATIC_LIBS) && !defined(Encodings_EXPORTS)
+		#pragma comment(lib, "PocoEncodings" POCO_LIB_SUFFIX)
+	#endif
+#endif
+
+
+namespace Poco {
+
+
+void Encodings_API registerExtraEncodings();
+	/// Registers the character encodings from the Encodings library
+	/// with the TextEncoding class.
+
+
+} // namespace Poco
+
+
+#endif // Encodings_Encodings_INCLUDED