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/callback.h

@@ -0,0 +1,78 @@
+#ifndef CPR_CALLBACK_H
+#define CPR_CALLBACK_H
+
+#include "cprtypes.h"
+
+#include <functional>
+#include <utility>
+
+namespace cpr {
+
+class ReadCallback {
+  public:
+    ReadCallback() = default;
+    // NOLINTNEXTLINE(google-explicit-constructor, hicpp-explicit-conversions)
+    ReadCallback(std::function<bool(char* buffer, size_t& size)> callback)
+            : size{-1}, callback{std::move(callback)} {}
+    ReadCallback(cpr_off_t size, std::function<bool(char* buffer, size_t& size)> callback)
+            : size{size}, callback{std::move(callback)} {}
+
+    cpr_off_t size{};
+    std::function<bool(char* buffer, size_t& size)> callback;
+};
+
+class HeaderCallback {
+  public:
+    HeaderCallback() = default;
+    // NOLINTNEXTLINE(google-explicit-constructor, hicpp-explicit-conversions)
+    HeaderCallback(std::function<bool(std::string header)> callback)
+            : callback(std::move(callback)) {}
+
+    std::function<bool(std::string header)> callback;
+};
+
+class WriteCallback {
+  public:
+    WriteCallback() = default;
+    // NOLINTNEXTLINE(google-explicit-constructor, hicpp-explicit-conversions)
+    WriteCallback(std::function<bool(std::string data)> callback) : callback(std::move(callback)) {}
+
+    std::function<bool(std::string data)> callback;
+};
+
+class ProgressCallback {
+  public:
+    ProgressCallback() = default;
+    // NOLINTNEXTLINE(google-explicit-constructor, hicpp-explicit-conversions)
+    ProgressCallback(std::function<bool(size_t downloadTotal, size_t downloadNow,
+                                        size_t uploadTotal, size_t uploadNow)>
+                             callback)
+            : callback(std::move(callback)) {}
+
+    std::function<bool(size_t downloadTotal, size_t downloadNow, size_t uploadTotal,
+                       size_t uploadNow)>
+            callback;
+};
+
+class DebugCallback {
+  public:
+    enum class InfoType {
+        TEXT = 0,
+        HEADER_IN = 1,
+        HEADER_OUT = 2,
+        DATA_IN = 3,
+        DATA_OUT = 4,
+        SSL_DATA_IN = 5,
+        SSL_DATA_OUT = 6,
+    };
+    DebugCallback() = default;
+    // NOLINTNEXTLINE(google-explicit-constructor, hicpp-explicit-conversions)
+    DebugCallback(std::function<void(InfoType type, std::string data)> callback)
+            : callback(std::move(callback)) {}
+
+    std::function<void(InfoType type, std::string data)> callback;
+};
+
+} // namespace cpr
+
+#endif