Merge pull request #30 from mlubin/master

small fixes to my post
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.