Improve documentation design

[lenkis]

Suggestions:

• Make TOC hide/show on demand + let the main text occupy more screen width
• Include all subsections in TOC (for convenience, maybe add expandable nested sections to the TOC, like in tarantool-c doc)
• Increase font size in func descriptions, both in text and auto-generated labels like "Parameters" (make it = general body text) - e.g. see the bug in https://tarantool.org/doc/reference_lua/msgpack.html?highlight=msgpack#module-msgpack
• Make vertical paddings before some paragraphs narrower:
  • before the first item in a bullet list
  • before parts of a func description (parameters, rtype, etc)
• Multiple functions definitions with one name - normal display
• Refactor .. varfunc:: -> italic in {}
• Center images in App D. Vinyl
• Cookbook - Every example must have links. Break it into chapters.

[lenkis]

comments to fix-markup branch:

1. can we decrease the lower padding after intro paragraphs before bullet lists? see green on the screenshot:

2. text in function descriptions is now smaller than body text, can we increase it to match body text? here's a screenshot to illustrate my concern:
   

[bigbes]

Probably done. ("Make TOC hide/show on demand + let the main text occupy more screen width" was moved to its own ticket gh-138)