Add artifact directory

GCryptLib/artifacts/optimization-performance-log.md

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+Old way (400 rounds, no matrix mult): 38.01s
+  400 was the minimum for good diffusion
+
+New way (10 rounds, with matrix mult): 1.16s
+  10 rounds now give sufficient diffusion
+  still using bitsets and strings
+
+With new block class (instead of bitsets) (10 rounds): 0.35s
+  still partially using bitsets and strings
+
+With new block class (6 rounds, still good diffusion): 0.21s
+
+With new templated block class (full block and half block): 0.14s
+  finally no more bitsets
+
+With new sbox, reduction, and expansion function: 0.03s
+
+With additional jumbling in feistel rounds: 0.03s
+
+With direct file reading/writing from data blocks: 0.02s
+