Created by: cvrebert
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
CC: @mdo for review