Misc old jpeg thigns from whenever I was last here.
Adding basic JFIF segment support.  At this point it's time to do some rearchitecting
Removing things not directly related to jpeg files
Started refactoring based on new architectural plan (get rid of constructors doing parsing, make validity contract better, use metatdata, and provide a generalized interface to segments, jpeg images and thumbnails
Refactoring package structure
Fix warning inf jfif density is 0
Tweaking parser