Better use of headings in Usage section

[wheresrhys]

I'd like to improve the headings in the Usage section of the docs to solve a few niggles:

• github's markdown styles don't contrast very much with each other once you get past h3
• Parameters is a subsection of a function's documentation and, as such, a heading rather than strong would be more semantic
• It's difficult to see where one section of API docs ends and another begins (for libraries that have multiple top level exports/classes)

Specifically, the changes I propose are

• Make API, Examples, Debug, Reporting Issues and LIcence into level 2 headings. It's debatable whether, semantically, these should live as subsections of Usage, but given the better UX when using higher level headings, it seems like a good call to prefer higher level headings where that choice can be made. A criticism of this is that arguably github should improve their low level heading styles, but I'm taking the pragmatic approach of trying to change one library rather than an entire website :-) . I will , nonetheless, raise the issue with github too
• Promote subheadings of API by 1 level to follow the promotion of the main API heading
• Make Parameters subheadings into proper headings instead of strong paragraphs
• Add HR after each top level section of the API docs

See developit/unistore#88 for an example of what the changes would mean

Any thoughts?

[tmcw]

🤔 Sure, I think that as long as this works well in-practice and improves readability, I'm all for it. Will need to take special care to make sure that the documentation readme isn't regressed, because I think it currently relies on all documentation output to be under an h2 and promoting individual sections to be at the h2 level will require a change in its splicing logic.