BS3: Move examples to @twbs/bootstrap-examples

Following our recent Glyphicons move, we're moving the examples to a separate repo as part of the [twbs organization](https://github.com/twbs/). **Here's why I think it's a great idea:**

- Bootstrap examples are built by treating Bootstrap as a dependency, meaning it's just using the compiled CSS and JS. This furthers that approach by separating them into separate repos.
- The examples included in the docs are rather simple, and as the community has shown, there are a lot more out there that could be better showcased. Why not have a repo that encourages folks to contribute their own examples?
- It **Removes All The Things™** from the repo, which is awesome from a focus and organizational perspective. It drops a dozen or so and removes hella code, keeping it lean and focused on the docs, CSS, and JS.
- This also, for now, keeps the examples as flat HTML files (no more Jekyll rendering for those). Much more accessible for folks who don't want to do the full setup.

Given how many folks have wanted more examples, or to add more examples, this move makes the most sense. It adds some overhead in copy-pasting the latest versions of the compiled CSS and JS over, but that's rather straightforward. Maintaining all those new examples that will hopefully come via PRs will take time to maintain, but we can deal with that as it arises (for now all will be updated to the latest versions).

[The new repo is already up and running](https://github.com/twbs/bootstrap-examples), with the latest changes and all the git history. All that remains on that end is creating the docs and publishing them like we've done with the [Glyphicons site](http://glyphicons.getbootstrap.com/).