switches 1.4.2, 4.1.0.21 to variables

[snostorm]

Not sure if you want this variation (if it stomps over the version output of your current build processes) but this is what my PR is using based off the subtree experiments. I can roll that part back for now if easier and you can ignore this :)

[Starefossen]

Just fyi, if this was site.current_version instead of project.current_version it would work seamlessly with Jekyll / Github Pages configuration variables from _config,yml. We are currently using the website branch as a submodule in gh-pages so this change may be a bit problematic for us atm.

[snostorm]

@Starefossen thanks for the heads up. I'm open to renaming this project-wide to help. For now, feel free to revert this locally if easier. This change was partially so I could experiment with a subtree update -- but also this is the pattern used for the other localizations at the moment.

Side question: is the main benefit you're getting from gh-pages additional publishing flexibility (specifically the blog section on iojs.no)? We're looking to try to work local groups to make sure we're meeting all the needs there from a iojs/website tech stack point of view, although it will still be up to localization teams if they wish to be published by us or not.