Needs to support scanning playlist files

Add CUnit to be built as a dependency when running make check

Portrait thumb sizes not correctly set (too tall)

Review thread safety for Progress/Error/Result instances

Keep track of memory diagnostics, add a memory limit feature like Image::Scale

valgrind testing
* memleak in recurse_dir

on_finish gets passed some stats about the scan:
* total number of new files
* total number of changed files
* total number of deleted files?
* time taken
* scanned items per second
* list of files with errors and error info?

Result should include a flag for indicating if the file is new, has changed, or was deleted

Perl: would_scan($file) - calls through to should_scan function

Support defining ignore lists on a per-directory basis

Clean up mediascan_linux/unix/macos/win32
