- Refer to the "slow" [I]DCT algorithms as "accurate" instead, since
they are not slow under libjpeg-turbo.
- Adjust documentation claims to reflect the fact that the "slow" and
"fast" algorithms produce about the same performance on AVX2-equipped
CPUs (because of the dual-lane nature of AVX2, it was not possible to
accelerate the "fast" algorithm beyond what was achievable with SSE2.)
Also adjust the claims to reflect the fact that the "fast" algorithm
tends to be ~5-15% faster than the "slow" algorithm on
non-AVX2-equipped CPUs, regardless of the use of the libjpeg-turbo
SIMD extensions.
- Indicate the legacy status of the "fast" and float algorithms in the
documentation and cjpeg/djpeg usage info.
- Remove obsolete paragraph in the djpeg man page that suggested that
the float algorithm could be faster than the "fast" algorithm on some
CPUs.