Implement progress output

GCryptCLI/include/ProgressPrinter.h

@@ -0,0 +1,23 @@
+#ifndef GCRYPTCLI_PROGRESSPRINTER_H
+#define GCRYPTCLI_PROGRESSPRINTER_H
+
+#include <iostream>
+#include "CommandlineInterface.h"
+
+// This class has the task to output progress to stderr, if requested
+class ProgressPrinter {
+  public:
+    //! Will print progress to stderr, if requested, and the interval matches
+    static void PrintIfAppropriate(
+      const std::string& message,
+      const std::size_t current,
+      const std::size_t target
+    );
+
+  private:
+    // No instanciation! >:(
+    ProgressPrinter() {};
+};
+
+#endif
+