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/Net/include/Poco/Net/QuotedPrintableDecoder.h

@@ -0,0 +1,86 @@
+//
+// QuotedPrintableDecoder.h
+//
+// Library: Net
+// Package: Messages
+// Module:  QuotedPrintableDecoder
+//
+// Definition of the QuotedPrintableDecoder class.
+//
+// Copyright (c) 2005-2006, Applied Informatics Software Engineering GmbH.
+// and Contributors.
+//
+// SPDX-License-Identifier:	BSL-1.0
+//
+
+
+#ifndef Net_QuotedPrintableDecoder_INCLUDED
+#define Net_QuotedPrintableDecoder_INCLUDED
+
+
+#include "Poco/Net/Net.h"
+#include "Poco/UnbufferedStreamBuf.h"
+#include <istream>
+
+
+namespace Poco {
+namespace Net {
+
+
+class Net_API QuotedPrintableDecoderBuf: public Poco::UnbufferedStreamBuf
+	/// This streambuf decodes all quoted-printable (see RFC 2045) 
+	/// encoded data read from the istream connected to it.
+	///
+	/// Note: For performance reasons, the characters 
+	/// are read directly from the given istream's 
+	/// underlying streambuf, so the state
+	/// of the istream will not reflect that of
+	/// its streambuf.
+{
+public:
+	QuotedPrintableDecoderBuf(std::istream& istr);
+	~QuotedPrintableDecoderBuf();
+	
+private:
+	int readFromDevice();
+
+	std::streambuf& _buf;
+};
+
+
+class Net_API QuotedPrintableDecoderIOS: public virtual std::ios
+	/// The base class for QuotedPrintableDecoder.
+	///
+	/// This class is needed to ensure the correct initialization
+	/// order of the stream buffer and base classes.
+{
+public:
+	QuotedPrintableDecoderIOS(std::istream& istr);
+	~QuotedPrintableDecoderIOS();
+	QuotedPrintableDecoderBuf* rdbuf();
+
+protected:
+	QuotedPrintableDecoderBuf _buf;
+};
+
+
+class Net_API QuotedPrintableDecoder: public QuotedPrintableDecoderIOS, public std::istream
+	/// This istream decodes all quoted-printable (see RFC 2045)
+	/// encoded data read from the istream connected to it.
+	///
+	/// Note: For performance reasons, the characters 
+	/// are read directly from the given istream's 
+	/// underlying streambuf, so the state
+	/// of the istream will not reflect that of
+	/// its streambuf.
+{
+public:
+	QuotedPrintableDecoder(std::istream& istr);
+	~QuotedPrintableDecoder();
+};
+
+
+} } // namespace Poco::Net
+
+
+#endif // Net_QuotedPrintableDecoder_INCLUDED