Exercise: Normalize filenames in subdirectories

[oleks]

When asked to submit a PDF report, students may pick wildly different filenames for the PDF.

Given a directory with a subdirectory for each student submission, normalize the directory structure such that all PDF files are named report.pdf.

Variations/caveats:

• There may be multiple PDF files in a student directory. Report an error for each directory where this is the case, or attempt to resolve the dispute.
• The PDF files may be hidden under ZIP files or further sub-directories.