The new package pkg/images/fastjpeg uses djpeg(1) to quickly
down-sample images at load time as described here:
http://jpegclub.org/djpeg/
Add benchmark comparing std lib jpeg.Decode and fastjpeg.DecodeDownsample
with a factor of 1, 2, 4, and 8.
Benchmark resizes a 4000x4000 pixel JPEG to 128x128.
Refactor in pkg/images to make images.Decode a little more readable.
Change-Id: I571db1f3c3068f99da4a01ec84fd246ef098a18c
Bill Thiede