Add more Checkstyle checks for AsciiDoc files
As a continuation of #257 (closed) where we enabled Checkstyle for AsciiDoc files, we should enable more checks:
Check to consider:
- Things we come up in issue #254, where we want to document the guidelines.
[source,not followed by a space.
- Headings: The first heading in a file should be level 2. All subsequent ones should be higher levels. Level increase should be from 2 to 3 to 4, not 2 to 4, although 4 to 2 is allowed. This should be able to handle
:leveloffset: +1etc as well.