Note that I decided that the Writer thing was a bit premature, so I cut
it out of ImageRepr. This inspired cleaning up the file and adding some
more documentation. As it stands in this commit the library will not compile.
Cleaned up the Devil backend mostly by commenting and removing some
exports. Do the same for JP backend.
Similarly cleaned up significantly the JuicyPixels backend, now to do
the same for 'Preview'
Cleaned up and commented the Preview file. Also removed the Writer
stuff, which was just unnecessary.