Create a RIFF/RIFX unarchiver

[dressupgeekout]

The .Dxr and .Cxt files in Secret Paths in the Forest correspond to Macromedia Director. However, Macromedia Director's files are implemented as RIFF archives (technically they're RIFXes to indicate the big-endian data contained within).

This means that, no matter what the bigger Director story ultimately is, we at a minimum have to have the ability to unpack RIFF archives. There definitely already exists code which can do this -- it's a very common archive format -- but I don't see any reason why Luna Purpura can't have its own implementation. This task should be very quick and straightforward.

More info: https://en.wikipedia.org/wiki/Resource_Interchange_File_Format