fix "Data attributes" link in JS docs sidenav

`#js-data-attributes` => `#js-data-attrs`
fix ID of Normalize heading in docs so that the sidenav can find it
Recess welcome
Merge pull request #8294 from cvrebert/patch-2

fix ID of Normalize heading in docs so that the sidenav can find it
Merge pull request #8291 from cvrebert/refactor

refactor responsive-utilities slightly
Move mixin to mixins.less
Merge pull request #8292 from cvrebert/patch-1

fix "Data attributes" link in JS docs sidenav
Merge pull request #8290 from juthilo/3.0.0-docs-nothird

Add new callouts to docs
Merge branch '3.0.0-wip' of github.com:twitter/bootstrap into 3.0.0-wip
Docs: create new callout classes
rm pre{white-space:pre-wrap;} since redundant to Normalize.css
rm fallback white-space for <code>

If my analysis is right, this should be unnecessary.
Merge pull request #8298 from cvrebert/patch-2

rm fallback white-space for <code>
Merge pull request #8297 from cvrebert/patch-1

rm pre{white-space:pre-wrap;} since redundant to Normalize
Spelling in comment
Fix typo in comment
Fix spelling in comment
Update mixins.less

Add a the function .make-small-column. See also http://stackoverflow.com/a/17308128/1596547
Fix 2 typos
rm :invalid styling from docs

It was removed from the code in 90d4343f66d1cdafe24b6de0dbb6ae64312df323  :-/