Exercises: Add plugin system task

exercises/task16/plugin.hpp

@@ -0,0 +1,19 @@
+#ifndef PLUGIN_HPP
+#define PLUGIN_HPP
+
+#include <memory>
+
+/// Interface for plugins.
+class Plugin {
+  public:
+	virtual void run() = 0;
+	virtual ~Plugin(){};
+};
+
+/// Symbol of the plugin constructor function.
+const auto PLUGIN_CONSTRUCTOR = "create_plugin";
+
+/// Type of the plugin constructor function.
+using PLUGIN_CONSTRUCTOR_T = std::unique_ptr<Plugin> (*)();
+
+#endif // PLUGIN_HPP