Return only files with valid Frontmatter

Objective:

Filter out any markdown files that have frontmatter content that could cause errors in another operation. Diagnose each error, and create a report listing all diagnosed errors. Return only files that have valid frontmatter to other functions that will perform operations on markdown files.

Constraints

Using only the fs and path node libraries, Process ALL files in a target directory, however nested. Any error should be non-blocking.