Fix various nits in markdown files

[jtraglia]

This PR touches a lot of files, but these were found somewhat organically and breaking it up into multiple commits and/or PRs would be very time consuming. This PR makes these notable changes:

• Delete unnecessary blank lines.
• Add blank line before code block or line, or between a header and a paragraph.
• Add missing table of contents headers.
• Move ToC headers to the correct location, out of doctoc section.
• Add work-in-progress notices to in-development specs.
• Remove work-in-progress notices from stable specs.
• Fix table whitespace/alignment issues.
• Left justify electra state list length unit fields.
• Where missing, add <!-- TOC --> comments for consistency.