General documentation style/source improvements

Things to consider:

• Styling
  • Proper/consistent use of layout macros, e.g. menu, kbd, btn.
  • Get rid of table/figure references and titles.
    • They are numbered in the single-page HTML output, and thus a bit weird if we split it and not renumber them. Also, for LaTeX that moves the figures around, references and titles make sense, but for AsciiDoc HTML/PDF output the order is as in the source file.
    • We can say things like "... as in the following figure:" and then immediately put the figure after that.
    • This mostly concerns Chi, but we should check all documentation sets.
• Documentation source layout
  • Everywhere exactly one empty line separation, except two empty lines before new section?
  • Single sentence per source line, for simpler reviewing (less irrelevant diffs).
• AsciiDoc features
  • Use * for unordered lists instead of -. See also #54 (comment 303258).
• Other
  • Use https instead of http in links where relevant.