[AD] Loader and saver formats

["Vincent Penquerc'h" <Vincent.Penquerch@xxxxxxxxxx>]

Title: Loader and saver formats

How about something along the lines of (very basic framework follows):

typedef enum {
  IMAGE_FORMAT,
  PALETTE_FORMAT,
  SAMPLE_FORMAT,
  FONT_FORMAT,
  MUSIC_FORMAT,
} FILE_FORMAT;

void register_format(FILE_FORMAT, void (*loader)(...), void (*saver)(...), int (*is_of_type)(...));
void unregister_format(FILE_FORMAT, void (*loader)(...), void (*saver)(...), int (*is_of_type)(...));

This would work like the current bitmap format registration routines
and allow other formats to be overriden as well.

The is_of_type callback would get called either with a filename, handle, or
already loaded raw data, and would test that format, returning a boolean.
Quite some casts would have to be done, but that's what the datafile routines
already do anyway.

--
Vincent Penquerc'h