unpack
Unpacks a NARC into a map of path → file data.
For anonymous NARCs (minimal FNT) the keys are the decimal file indices ("0", "1", …). For named NARCs the keys are slash-separated paths such as "sprites/player.ncgr".
Return
A map from path (or index string) to file contents.
Parameters
data
The raw NARC bytes.
Throws
Illegal
if the data is not a valid NARC container.