Add rake task for updgrading JB versions

[plusjade]

There is no obvious way to upgrade Jekyll-Bootstrap versions.

[adelevie]

What's the non-obvious way?

[plusjade]

You can add jekyll-bootstrap as a remote to your repository, fetch it, then compare it to your HEAD. This is better outlined here: https://github.com/plusjade/jekyll-bootstrap/pull/35

There are 4 main integration points between Jekyll-Bootstrap and Jekyll.

• _config.yml
  There are still some variables in use that are not namespaced into JB hash. But ideally we'll place every variable in JB and then find a clean way to merge the file without reorganizing the user data.
• _includes/JB
  These files are properly namespaced. You should always override the methods as outlined here: http://jekyllbootstrap.com/api/bootstrap-api.html#method_overrides rather than edit the files directly so this should be easily upgradable.
• Rakefile
  The Rakefile can be upgraded cleanly, provided we add this feature in: https://github.com/plusjade/jekyll-bootstrap/pull/33 which allows users to extend the rakefile freely with their own tasks.
• Themes
  Themes should be namespaced and versioned independently from the JB core so with the exception of a major version release the theme API should not be affected at all when updating.

Are there any more areas I've missed? Ideally we need to fully automate this task. However it's better to not do anything than to risk overwriting user data. So I want to make sure to avoid any such possibility.

I would like to hear your thoughts on this, thanks!

[wizardishungry]

The upgrade guide from #35 appears to have gone missing.