Blog posts on building GUIs

I finally finished an image viewer GUI, and perhaps more importantly decided to write a pair of blog posts introducing graphics with Tk and Cairo.

This currently requires using master of the following packages: Tk, Cairo, Images. There's also a new repository not yet packaged, `git@github.com:timholy/ImageView.jl.git`. It seems possible that some of this code (particularly the rubberband) may be of general interest and should live somewhere else.

Comments on the blog posts, or packages, would be appreciated. My hope is that we can bump the package shas on Tk and Cairo soon so I can package ImageView. Any objections to doing that?