File (re-)assembly

[PaulusParssinen]

Add methods to ShockwaveFile to allow (re)assembly of directory authored files. The methods on ShockwaveFile are the low-level API which just blits the movie/cast resources to output from memory, without performing any resource pointer i.e. indice fix-ups.

I've been thinking of the way to structure more higher-level API that does more logic to trim various unnecessary resources and handles the "pointers" without library consumer having to worry about them. But that'll be follow-up and lower priority due to its complexity.