Some of the snippets need to be updated later.

* Prep for v4.3.0

* More updates for v4.3.0.

* rerun to build docs source map

Update nuspec and build script to support `<license />` instead of the deprecated `<licenseUrl />`

- Move 4.1 docs to 4.2
- Update versions everywhere to 4.1.3 with release script
- Manually bump the shorthand version in package.json
- Add 4.2 to the versions docs page
- Update some redirects
- Fix tests asset URLs
- Bump Nuget and more

With the current docs directory setup, I'm making too many mistakes and have to manually address path changes and directory moves on deploy. This makes for a frustrating experience developing locally and shipping releases. With this PR, we're basically back to the same setup from v3—duplicating the dist directory into our docs directory. Not the most ideal, but very straightforward for me as the release manager.

* Update copyright range to include 2018

* Extend copyright date range on new files from 2017 to include 2018

* 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

https://github.com/twbs/bootstrap/issues/22359

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* bower.json, package.json: Extend jQuery version ranges to include v3
* NuGet: Bump jQuery to v3.0.0.1
* Docs+Examples: Update jQuery to v3.0.0
* Use jQuery v3.0.0 for JS unit tests
* Update jqueryVersionCheck to allow jQuery v3.x.x

️️️ https://github.com/twbs/bootstrap/graphs/contributors

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