clarifies that normalize.css is a dependency of reboot

Media vertical align flexbox classes

v4 - Force linebreaks after grid tier names in v4 grid docs

v4 - Fix link to narrow jumbotron example

v4 - Updated default navbar example to use responsive navbar

Combine size & square mixins into one

Update static form control example

Remove CSSLint references.

Document utility class .bg-inverse

v4: Conditional predefined grid classes

Semantic grid: add make-container-breakpoint

Fix several erroneous links in docs.

Fixed link to nav component from scrollspy documentation

Adds table-responsive class to docs table

(reported by ianhernandez in Slack)

Remove the unused Google fonts.

Apply !default to SCSS variables

Missed one variable :(

Accept elements as the tooltip / popover content

When a DOM node is passed to an HTML tooltip, the `title` node is only
moved if it is not already in the tooltip. Otherwise, `empty()` is used
instead of `detach()` before appending the `title` to avoid memory
leaks. If a DOM node is passed to a plain text tooltip, its text is
copied via jQuery `.text()`.

Replaces `.detach()` with `.empty()`, as `.detach()` is almost never
useful but instead leaks memory. The difference between `empty` and
`detach` is that the latter keeps all the attached jQuery events/data.
However, since we do not return the previous children, the user would
have to keep these themselves, thus they can `detach()` if necessary.

This is a port of https://github.com/twbs/bootstrap/pull/14552 to v4.

[ci skip]

Use `https` when possible.

rm unused $state param from form-control-validation mixin

[ci skip]

[ci skip]

[ci skip]

Fix the JS errors due to jekyll-search.

Remove the now unused grunt-contrib-jade references.

Related to #17314.