fixes #13216

By definition, XS screens have no minimum size, only a maximum size.
(Symmetrically, LG screens have no maximum size, hence why there's no @screen-lg-max.)

explicitly doc that icon classes should only be used on empty elements

Add comments in carousel.js to clarify that "slid" is not a typo

Addresses #13248.

add document ready jQuery wrapper in Android Browser workaround

Closes #13103 by merging it.

doc that popover content() is given the element as an arg

change `@zindex-popover` and `@zindex-tooltip` values to be greater than
those set for `@zindex-modal` allowing tooltips and popovers to be
displayed in front of modals (and all other content).

Fix customizer (see #13043)

Add Gist & Customizer URLs to customized files & config.json

Fixes #9951
Fixes #12865

- Move example to correct location docs/examples/
- Move custom JS and CSS into stand-alone files
- Update headers and footers
- Copy-editing

Update normalize.css to v3.0.1

The Google Analytics account we use cannot currently be upgraded to Universal Analytics. In order to keep using Analytics, we have to stick with Classic for now.

fix doc typo

one can find correct name of variable just few lines below the typo