Additional changes for Dev Docs

[kahboom]

Some changes:

• Temporary admonition, code block workaround for Markdown, add asciidoc SCSS file for now.
• Remove "Code" from top navigation bar, as this is already linked to from the Octocat at the top, and the footer.
• Octocat rel="nofollow" for SEO, open in new tab
• Several typo fixes, broken links, internal relative links not working, CSS/padding fixes

Would like to resolve the issue with the table cell background colors, but this may be a futile effort if we are intending to do major changes to the website in the near future (e.g. switch framework or formatting tool). Also a low priority.

[pure-bot[bot]]

Pull request approved by @KurtStam - applying approved label