* Consolidate the security concept pages into a single page.
- This updates the security concept material to be on a single page, which matches the
change done last week for the rest of the concept material. This ends up being a less clicky
more directed introduction for newcomers to the platform.
- While I was there, I moved the redundant What is Istio page from our about section and stuck
the content at the top of the What is Istio page in the Concepts section.
- Add <github_file> <github_blob> and <github_tree> to make it simpler to link to the right
place on GitHub.
- Use these new sequences throughout the docs.
- Also, fix bad HTML generated for the TOC in certain cirsumstances.
- Fix extra blank line inserted at the bottom of indented code blocks.
- Remove What's next sections since we now have auto-generated See also sections
- Fix a few incorrectly capitalized headers, "istio", "kubernetes", "sidecar"
Martin Taillefer
Frank Budinsky
mtail