Fix inconsistent markdown formatting.

This changes all of the documentation markdown files to follow
the same rules. The rules I've applied are from
https://github.com/DavidAnson/markdownlint/blob/v0.25.1/doc/Rules.md

The reason I felt it was necessary
to change all the files was
that there were a lot inconsistencies in how the markdown was used.
Ranging from header levels to some headers having a new line before
content and some not.

docs/pages-and-sections.md

@@ -57,7 +57,6 @@ Only top-level fields supported by sub-pages are `pageInfo` and `sections`. The
 
 Note that since page paths are required by the router, they are set at build-time, not run-time, and so a rebuild (happens automatically) is required for changes to page paths to take effect (this only applies to changes to the `pages` array, rebuild isn't required for editing page content).
 
-
 ## Sub-Items
 
 A normal section will contain zero or more items, for example: