SlowRiot authored Dec 21, 2021 and freetrader committed Dec 21, 2021

One of a multi-part series of changes to improve markdown code quality,
primarily driven by feedback from codeclimate's markdownlint plugin.

This MR fixes markdown whitespace issues flagged by markdownlint:

* Whitespace around headers
* Whitespace around lists
* Remove duplicate empty lines
* Consistent list indentation (two spaces for indented sub-lists)
* Remove trailing whitespace
* Misc whitespace tidying

Test Plan
---------

- review document changes
- run ninja doc-html on master, take a backup, and run it again on this branch
  - run recursive diff to verify no unexpected changes appear in the
    generated html
  - for files where differences occur, compare changed locations in generated
    doc/html/index.html with a browser to content generated on master, and to
    content on https://docs.bitcoincashnode.org
    (not all changed documents are present there, the ones that are not can be
    treated as out of scope of this compari...