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/fyi @mdo

Fix #17166

Fix #17052

- new vars for .lead size and weight (previously had none)
- new var for default margin-bottom on h1-h6 elements (previously had none)
- rearranged vars to combine two typography sections into one in variables.scss
- reassigned border-width var to hr-border-width
- made hr-border more specific as hr-border-color

Use grid classes or mixins on .dl-horizontal, update docs to include it, removes auto truncate and makes .text-overflow mixin into a .text-truncate class and mixin combo for better granularity

New text align class, .text-nowrap, for preventing text from breaking to new lines. Applies it to the grid docs table.

Transform text in components with text capitalization classes.

For better readability on mobile devices