Update to version 0.8.1
    
    Drop patch xxhash-pkgconfig-version.patch (accepted upstream)
    Fix compilation on RHEL 7 ppc64le (gcc 4.8)
    The x86 dispatch code now enables sse2 and avx2 separately, it can now use
      sse2 on EPEL 7 without trying to use avx2 which is not supported by gcc 4.8
    Add documentation package - doxygen mark-up was added