Ensure that all TA article files are actually checked

[RobH123]

From a question on Discord from @mandolyte: Question for you... when we add validation for markdown TA articles, how do you recommend doing it...

• do we give the folder name and let CV get and validate the three files?
• do we combine all three files in memory and give that to be validated?
• do we give each of the three files in turn to be validated?

This is because TA articles have three files:

1. 01.md
2. title.md
3. sub-title.md

So it seems that:

1. We need to discover whether or not all three files are being checked for TA articles
2. Might be good to have an exported function that is passed an article name/folder, and checks the three files (and that's there's three and only three in the folder)