Document what waring_level 1,2,3 means.
Test if markdown files are in sitemap
Add Builtin-options.md to sitemap.txt
Builtin-options.md:
Fix tables in Builtin-options.md
Add documentation for warning options
Added more options to doc
General documentation:
Add link to Builtin-options
Remove obsolete file
Testing:
Add function test_markdown_files_in_sitemap.
Checks if each markdown file is contained in sitemap.txt