code: def filter_filenames(filenames):
      
      filenames_cleaned = []
      for filename in filenames:
          keep = True
          for pattern in FILE_EXCLUDE_EXTENTIONS:
              if filename.endswith(pattern):
                  keep = False
          for pattern in FILE_SKIP_PATTENRS:   # This will reject exercises...
              if pattern in filename:
                  keep = False
          if keep:
              filenames_cleaned.append(filename)
      return filenames_cleaned
docs: Skip files with extentions in `FILE_EXCLUDE_EXTENTIONS` and filenames that
      contain `FILE_SKIP_PATTENRS`.