* Offset option can be function (Popper.js)

* Fix...add function type for offset option

* Remove constants for popper config

* Optimize code. Remove foreach loop.

* Refactoring. Remove getOffset method

* Fix media-breakpoint-between

When compiling .scss that uses media-breakpoint between with xs as the lower bound or xl as the upper bound, a compilation error can occur due to $min/$max being set to null, or the resulting .css can be invalid (see issue #23965).

(This is basically the same fix that was applied to media-breakpoint-only a short time ago).

* Update _breakpoints.scss

Make houndci-bot recommended changes.

Nav Pills with open dropdown don't reflect the nav-pills active state. The active state should also be reflected when using collapse plugin inside nav-pills.

https://github.com/twbs/bootlint/wiki/W007

* Add first class to grid framework to add negative ordering

* Add order-first explination to the docs