Fixed link.
Better base `ul` and `ol` styles

Turns out we were nixing the default browser spacing for bullets and
numbers, so this reverts that and instead just twerks the top/bottom
`margin`.
Remove explicit, unncessary `line-height` on `li` elements
Properly unstyle the `.list-unstyled` class by switching from `margin` to `padding`

Also add better comments
Better clearing on `.dl-horizontal` for empty `dd` elements

Instead of clearing the entire `.dl-horizontal`, we've moved the
clearfix mixin to the `dd` level to solve two problems in one: empty
`dd`s mid-list, and empty `dd` as the last child.

Addresses a few old issues, including #2824, #3819, #3821, #4062,
#6707, and #7180.

Sorry that took so long :D.
Fixes #7599: Improved print styles for a few key components

* Updates `.table` to always enforce a solid white background
* Update button groups and dropdowns to always use black carets
* Add a 1px solid black border to labels (in the future we should add a
border to these perhaps for better printing)
Merge pull request #8182 from karelvuong/3.0.0-wip

3.0.0-wip - Fixed 'Running Doc. Locally" Link
Add note about Jekyll version per #8195
Addresses #8199: darker default button
Merge pull request #7 from twitter/3.0.0-wip

3.0.0 wip