Add favicon for docs
Documentation link fixes

External
- Create :wiki: extlink for remaining wiki docs
- Use :wp: extlink
- Fix some broken :wp: links

Use own link text to prevent strange page header text appearing for
links.
Add ignore for linkcheck
Remove version info in text
Improve documentation formatting

- Use :menuselection:, :kbd: and :envvar: markers
- Correct code highlighting format
- Use inline text when needed
- Convert list to more readable table
Highlight setting names and files