Improve heading depth test
What does this MR do and why?
What
Changes the Vale "heading depth" test so that it warns of headings at table of contents (TOC) depth 6 and above.
Why
The rule flags instances of H5-level headings (#####) as failing this rule/test. For example, in VS Code a user sees the following message, which is incorrect. This MR ensures that only headings of H6 level and above are flagged.
Edited by Russell Dickenson