Add extraction for release dates for the new-format (at least) ninjatune xls files

Mostly putting up for review for the sake of this being a way to have people able to question my stuff and learn about the codebase.

This parses out the release dates in the newer of the two ninjatune xls formats (the old one has strings, as I recall, and I'm not sure it splits by country -- I haven't checked yet).
I guess this is a function because the SimplePathPart instances are mutable/need to be unique? Speaking of those, I don't really understand what they do. :P

Does every "part" of the destination get converted into a PathPart instance (i.e. 'release', 'events', 'combined', (0, 'Main')) if it's not already, and then get linked with the others somehow to store the mapped data?

What does no_manip do?