Changes for generalized runtime SSE/AVX/XOP detection.
Multi instruction set XXhash build with runtime selection.
Extend CPUID code to detect more instruction sets.
Add options for BLAKE2 hash.
Move GCC builtins into utils header.
Bump file format version number due to extended digest flags.
Add descriptions to digest list.
Major changes to use Intel's optimized SHA512 code for SHA512 and SHA512/256.
Remove earlier SHA256 code which is slower than SHA512/256 (on 64-bit CPU).
Use HMAC from Alan Saddi's implementation for cleaner, faster code.
Add optimized BLAKE2 implementations with runtime detection of CPU capability (SSE/AVX).
Minor cleanups.
Update default checksum to BLAKE256.
Use BLAKE2 parallel version for single-chunk archives (whole file in one chunk).
Set decompression threads correctly for single-chunk archives.
Add parallel versions of various checksums for single-segment, single-thread compression.
Fix return from parallel versions of Keccak_Hash() function.
Merge pull request #1 from moinakg/master

Merge