Prep for v4.2.0 release

- 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

package.js

@@ -5,7 +5,7 @@
 Package.describe({
   name: 'twbs:bootstrap',  // https://atmospherejs.com/twbs/bootstrap
   summary: 'The most popular front-end framework for developing responsive, mobile first projects on the web.',
-  version: '4.1.3',
+  version: '4.2.0',
   git: 'https://github.com/twbs/bootstrap.git'
 });