add callback blog draft
Now that Gaston is supported on master, nudge people towards using Gaston first for graphics.
Merge branch 'master' of github.com:JuliaLang/julialang.github.com
Merge branch 'master' of https://github.com/JuliaLang/julialang.github.com
rename callback blog post for release today
Merge pull request #31 from stevengj/master

possible blog post on passing Julia functions as C callbacks
shorter title
Merge branch 'master' of https://github.com/JuliaLang/julialang.github.com
shelling out: fix output from second non-existent dir example.
typo
typo
use cglobal rather than dlsym
Blog post on GUIs
Add formatting, title, author
A few tweaks to the starting sentences
Add more figures, and revise text
Add calls to Tk.update() and simplify bind() syntax
Update to changes in infrastructure
Add link for teaching material.
Merge branch 'master' of github.com:JuliaLang/julialang.github.com