Libjpeg-turbo

At least we have ubiquitous ARM now, if you want to test your code on non-x86 platforms.

> libjpeg/SIMD predates libjpeg v7 by several years, which means that our SIMD extensions are not compatible with some of the new features in libjpeg v7 and v8. Thus, merging with the upstream libjpeg code would have been very difficult, if not impossible (more recent comments by the current maintainer of libjpeg indicated that our SIMD extensions would not have been accepted, anyhow.)

> In fact, since jpeg-7, every new release of the IJG's software has broken backward ABI compatibility with prior releases (needlessly, in the case of jpeg-9), and both jpeg-8 and jpeg-9 introduced new, non-standard image formats that couldn't be decoded by previous IJG releases or by other JPEG codecs.

> When compared to baseline (the only mode that is fully accelerated in libjpeg-turbo), the combination of progressive JPEG, jpgcrush, and trellis quantization improved the compression ratio by 15-27% (average 20%) in our testing but increased encoding time by approximately 34-59x. More than half of the compression ratio improvement came from the use of progressive JPEG, which is supported in libjpeg-turbo as well. Decoding time was increased by anywhere from 17% to 3x, with most of this again being due to the use of progressive JPEG.