int save_bitmap(const char *filename, BITMAP *bmp, const RGB *pal);
DESCRIPTION
Writes a bitmap into a file, using the specified palette, which should be
an array of 256 RGB structures. Returns non-zero on error. The output
format is determined from the filename extension: at present this
function supports BMP, PCX and TGA formats.
Two things to watch out for: on some video cards it may be faster to copy
the screen to a memory bitmap and save the latter, and if you use this to
dump the screen into a file you may end up with an image much larger than
you were expecting, because Allegro often creates virtual screens larger
than the visible screen. You can get around this by using a sub-bitmap to
specify which part of the screen to save, eg:
