No more Ruby dependency and most important more than 10 times less build time (at least on Windows)!

This reverts commit 11da1601.

This is no longer needed with jekyll-toc 0.9.1.

Callouts are already excluded from ToC, but due to a limitation in jekyll-toc they are still being included.

We should revisit this if the bug is fixed later.

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.

Also fix a couple of typos while at it and change header tags' order.