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/CPR/include/cpr/unix_socket.h

@@ -0,0 +1,21 @@
+#ifndef CPR_UNIX_SOCKET_H
+#define CPR_UNIX_SOCKET_H
+
+#include <string>
+
+namespace cpr {
+
+class UnixSocket {
+  public:
+    // NOLINTNEXTLINE(google-explicit-constructor, hicpp-explicit-conversions)
+    UnixSocket(std::string&& unix_socket) : unix_socket_(std::move(unix_socket)) {}
+
+    const char* GetUnixSocketString() const noexcept;
+
+  private:
+    const std::string unix_socket_;
+};
+
+} // namespace cpr
+
+#endif