Multimedia: JPEG compression using Lepton

[M-Gonzalo]

Besides being able to compress baseline and progressive jpg images using a dedicated method, Fairytale should be also capable of re-compress jpg images that use arithmetic coding. For that we can't count on packJPG but we can use the Lepton library, a tool released by the Dropbox team. It can also serve as a drop-in replacement for the packJPG library, should it fail on a certain stream.