Currently, auto placement is using the container dimensions (if provided) or the element's parent to determine where to open the tooltip:
```javascript
var $container   = this.options.container ? $(this.options.container) : this.$element.parent()
var containerDim = this.getPosition($container)
```
This is quite broken in fact, because the parent element could be just a small div outside the element for example, leading in a totally random placement (placing the tooltip on top even if there's no room). And the container can also be outside of the viewport.

This fix simply uses the viewport instead, that's the purpose of the viewport actually, to position the tooltip.
So the auto placement should use it to find where there's more room.
By default this is body, which is good.

add role="button" to a[data-toggle="collapse"]

Add aria-expanded to navbar toggles

Also, use id rather class name for the navigation, as it's unique and
lets us use correct aria-controls (and without the use of id,
aria-expanded does not get updated correctly by the current dropdown
toggle script)

Callout for tooltips and keyboard/AT accessibility

Before, most callouts hierarchically came under Examples > Four
directions, which is not appropriate. Now they're under Markup

Include callout explicitly mentioning tooltips should only be added to
focusable elements. Closes #16134

Closes #16073 by merging it

Increment quick start options to six in readme.md

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Closes #16113
Closes #16114

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Add `.alert-warning` related change to migration doc

avoid unnecessary HTML string building+parsing

Update jspm configuration

Refs #15947

ScrollSpy: Fixed proper nav element selection when scrolling upwards

bootstrap-sass v3.3.2 is broken.
Refs https://github.com/twbs/bootstrap-sass/issues/862
Refs https://github.com/twbs/bootstrap-sass/releases/tag/v3.3.3
Refs https://github.com/twbs/bootstrap-sass/commit/daeb43dcc7b0ab06328acaca0549ee68c039aaa6

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