Having it uppercase doesn't offer anything and the lowercase version slightly improves gzip compression.

* use a trailing slash when possible
* use https when possible
* remove a few redirected links
* consistently use `https://popper.js.org/`
* fix `iconUrl` in nuget files
* change Jekyll Windows guide to the official one

* Fix incorrect code indentation
* Remove unnecessary vendor prefix for `box-sizing` - all modern browsers now support this unprefixed
* Remove incorrect `<label>` and change static controls to readonly inputs
* Allow `<img>` elements without `src` to allow for `holder.js` images used in the docs, which lack `src` and use `data-src` instead

* Get this party started by removing mention of Normalize.css

* Nuke the old comment, consolidate to a single line and number as appropriate

* Bring over styles for HTML element from Normalize to Reboot

* Move margin override for body element from Normalize to Reboot

* Drop the block reset for HTML5 elements in IE9- from Normalize given we dropped IE9 support

* Building on previous commit, do the same thing for figure, figcaption, and main

* Remove IE9- display from Normalize given our browser support

* Drop IE8 figure margin because we're IE10+

* No need for the h1 overrides because we reset these font and margin styles anyway in _type.scss already

* Drop Safari 6 b and strong normalization because we're Safari 8+

* Remove mark styles for IE9- from Normalize

* Remove old iOS audio fixes from Normalize

* Remove IE9- display for progress from Normalize

* Remove more IE9- rules from Normalize

* One more IE9- display removal for canvas element

* Move pre overrides from Normalize to Reboot

* Move over some link resets to Reboot, drop others

- Move over background-color and text-decoration
- Drop focus outline change given it affects the offset on hover of
focused links

* Move over more code element resets, consolidate with pre overrides, too

* Move over sub and sup wholesale

* Move over img normalization to Reboot

* Move over SVG override too

* - Drop dupe hidden, but add comment for it
- Move over template
- Move over summary

* Remove bulk of @viewport comment

* edit down that code comment

* consolidate html-based normalizations

* update comments

* Consolidate abbr styles

* move over more type elements

* move over hr changes

* move over form controls and more

* move over button resets

* move over firefox button changes

* move over search changes and more

* we nuke all these styles for fieldsets anyway, so outright remove them

* no need for those, we override them

* move over legend, fieldset, progress

* line break

* delete normalize file

* linting

* update comment

* clarify docs mentions of normalize and reboot

* remove normalize excludes from linter

* remove normalize excludes from cli task

* linting

* callout license since we forked part of normalize

* Improve comments, move table background reset to .table class instead of in reboot

* trailing space

* Remove IE compatibility mode meta tag from docs, examples, and JS tests as we no longer support IE9 and IE8
* update and remove some IE bits from our supported browser page
* update introduction.md to match
* reword starter template intro

* descriptions for getting started pages

* descriptions for layout

* add content page descriptions

* more descriptions, updates to some existing ones

* correct site url

* add social stuff to config for twitter cards

* add twitter meta tags; use large image for homepage and regular card for all others

* add the assets

* more site config

* more social shiz to partial, remove existing meta for the partial, remove page title from homepage for simpler if statements

Remove 'including'.

[skip sauce]

This reuses the existing URLs in the docs Jekyll configuration rather than hard coding.

[skip sauce]

See https://github.com/twbs/bootstrap/pull/17793#issuecomment-146960473

Related to #17314.

Mostly links.
Fixes #17056.

Fixes #17096