Doxygen adjustment, and better directory name for GCryptLib

GCryptLib/include/Config.h

@@ -0,0 +1,10 @@
+#pragma once
+#include <cstddef>
+
+namespace Leonetienne::GCrypt {
+  // MUST BE A POWER OF 2 > 4
+  constexpr std::size_t BLOCK_SIZE = 512;
+
+  // MUST BE > 2
+  constexpr std::size_t N_ROUNDS = 64;
+}