* Allow url(), attr(), none,... as breadcrumb divider
* Update breadcrumb divider docs

* add margin variable for breadcrumb

* add margin variable for breadcrumb correction

* breadcrumb margin variable changes after review

* Drop -x and -y as they're all the same
- Also move -width to elsewhere in the vars because it makes no sense by spacers.
- Update values of -x and -y across main Sass and docs Sass.
* Update docs to reflect changes; link to spacing utils from options page

In IE9-11, prevent breadcrumb separator from getting underlined on :hover when not using <ol> markup

Fixes #18733 in IE9-11
Also adds comments to the code explaining this and #18740.

In modern browsers, prevent breadcrumb separator from getting underlined on :hover when not using <ol> markup

Fixes #18733, except in IE9-11
Closes #18740

Use new `.breadcrumb-item` class instead of child selectors and `li` tag selectors,
so as to no longer require the usage of `<ol>`-based markup.

Rename variables to follow naming conventions:
* $breadcrumb-padding-vertical => $breadcrumb-padding-y
* $breadcrumb-padding-horizontal => $breadcrumb-padding-x

Introduce new variable: $breadcrumb-item-padding

[skip sauce]

Fix #17052

We have it set to `1` right now just to avoid compilation errors, but
it’s been replaced everywhere with our new spacer classes anywho. We’ll
likely want to remap that var to custom component vars though (e.g.,
`$pagination-margin` instead of `$spacer-y`).