Spacing SASS backwards port from Bootstrap 4 to 3

Make use of Bootstrap 4's spacing utilities.

npm i spacing-bootstrap-3

@import 'node_modules/spacing-bootstrap-3/spacing';
@import '~/spacing-bootstrap-3/spacing';

You can now use any spacing utility classes like:

<div class="p-1 py-sm-2 mb-lg-3"></div>

It actually uses linear increments for the spacings, based on the $grid-gutter-width by default, rather than bootstrap 4's bonkers built in one (which I've whinged about, but Mark Otto isn't having any of it).

Howsoever, you can easily override the defaults by setting a $spacers map variable.