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/Foundation/include/Poco/Timezone.h

@@ -0,0 +1,67 @@
+//
+// Timezone.h
+//
+// Library: Foundation
+// Package: DateTime
+// Module:  Timezone
+//
+// Definition of the Timezone class.
+//
+// Copyright (c) 2004-2006, Applied Informatics Software Engineering GmbH.
+// and Contributors.
+//
+// SPDX-License-Identifier:	BSL-1.0
+//
+
+
+#ifndef Foundation_Timezone_INCLUDED
+#define Foundation_Timezone_INCLUDED
+
+
+#include "Poco/Foundation.h"
+#include "Poco/Timestamp.h"
+
+
+namespace Poco {
+
+
+class Foundation_API Timezone
+	/// This class provides information about the current timezone.
+{
+public:
+	static int utcOffset();
+		/// Returns the offset of local time to UTC, in seconds.
+		///     local time = UTC + utcOffset() + dst().
+		
+	static int dst();
+		/// Returns the daylight saving time offset in seconds if
+		/// daylight saving time is in use.
+		///     local time = UTC + utcOffset() + dst().
+	
+	static bool isDst(const Timestamp& timestamp);
+		/// Returns true if daylight saving time is in effect
+		/// for the given time. Depending on the operating system
+		/// platform this might only work reliably for certain
+		/// date ranges, as the C library's localtime() function
+		/// is used.
+		
+	static int tzd();
+		/// Returns the time zone differential for the current timezone.
+		/// The timezone differential is computed as utcOffset() + dst()
+		/// and is expressed in seconds.
+	
+	static std::string name();
+		/// Returns the timezone name currently in effect.
+		
+	static std::string standardName();
+		/// Returns the timezone name if not daylight saving time is in effect.
+		
+	static std::string dstName();
+		/// Returns the timezone name if daylight saving time is in effect.
+};
+
+
+} // namespace Poco
+
+
+#endif // Foundation_Timezone_INCLUDED