* Adding blake2b test function to src/tests/hash
* New files for testvector.
* Adding the test to CMakeLists.txt
* Adding brief documentation for the test.
Contains two modifications to improve ASIC resistance: shuffle and integer math.
Shuffle makes use of the whole 64-byte cache line instead of 16 bytes only, making Cryptonight 4 times more demanding for memory bandwidth.
Integer math adds 64:32 bit integer division followed by 64 bit integer square root, adding large and unavoidable computational latency to the main loop.
More details and performance numbers: https://github.com/SChernykh/xmr-stak-cpu/blob/master/README.md
hash: add prehashed version cn_slow_hash_prehashed
slow-hash: let cn_slow_hash take 4th parameter for deciding prehashed or not
slow-hash: add support for prehashed version for the other 3 platforms
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