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/packaging/README.txt

@@ -0,0 +1,24 @@
+ POCO C++ Libraries
+==================
+
+POrtable COmponents C++ Libraries are:
+--------------------------------------
+- A collection of C++ class libraries, conceptually similar to the Java Class Library, the .NET Framework or Apple<6C>s Cocoa.
+- Focused on solutions to frequently-encountered practical problems.
+- Focused on <20>internet-age<67> network-centric applications.
+- Written in efficient, modern, 100% ANSI/ISO Standard C++.
+- Based on and complementing the C++ Standard Library/STL.
+- Highly portable and available on many different platforms.
+- Open Source, licensed under the [Boost Software License](https://spdx.org/licenses/BSL-1.0).
+
+----
+To start using POCO, see the [Guided Tour](http://pocoproject.org/docs-1.5.3/00100-GuidedTour.html) and [Getting Started](http://pocoproject.org/docs-1.5.3/00200-GettingStarted.html) documents.
+
+----
+POCO has an active user and contributing community, please visit our [web site](http://pocoproject.org), [forum](http://pocoproject.org/forum) and [blog](http://pocoproject.org/blog). 
+Answers to POCO-related questions can also be found on [Stack Overflow](http://stackoverflow.com/questions/tagged/poco-libraries).
+
+----
+In regards to Boost, in spite of some functional overlapping,
+POCO is best thought of as a Boost complement (rather than replacement).
+Side-by-side use of Boost and POCO is a very common occurrence.