I tried to work out what was "Xtra", looked like just Icon Buttons. Then realised it says at the top "Bootstrap Xtra inludes extra features that are not included in Bootstrap but may be useful for some people. Xtra Features: Icon Buttons."
This really seems like something that should be in the scope of a pull request, or several of those.
Good idea to expand on Bootstrap, taken how popular it is. However the only addon here seem to be the buttons. And the example link on top links to the normal bootstrap, not this new version.
I think this should more like bootstrap-btns something I can include along side the original bootstrap.