doc: tweak markdown quoting
doc: tweak Markdown header syntax
doc: tweak Markdown to use `<kbd>` tag
doc: make "See Also" always a bulleted list
doc standardize quoting + install instructions
improve `set-fontset-font` recommendation

- use`font-spec`
- use trailing colon for disambiguation
doc: improve Markdown quoting
doc: TOC, list formatting
travis-lint no longer permits language emacs-lisp