pngchange.txt - changes for libpng

version 0.2
	added reader into png.h
	fixed small problems in stub file
version 0.3
	added pull reader
	split up pngwrite.c to several files
	added pnglib.txt
	added example.c
	cleaned up writer, adding a few new tranformations
	fixed some bugs in writer
	interfaced with zlib 0.5
	added K&R support
	added check for 64 KB blocks for 16 bit machines
version 0.4
	cleaned up code and commented code
	simplified time handling into png_time
	created png_color_16 and png_color_8 to handle color needs
	cleaned up color type defines
	fixed various bugs
	made various names more consistant
	interfaced with zlib 0.71
	cleaned up zTXt reader and writer (using zlib's Reset functions)
	split transformations into pngrtran.c and pngwtran.c
version 0.5
	interfaced with zlib 0.8
	fixed many reading and writing bugs
   saved using 3 spaces instead of tabs
version 0.6
   added png_large_malloc() and png_large_free()
   added png_size_t
   cleaned up some compiler warnings
   added png_start_read_image()
version 0.7
   cleaned up lots of bugs
   finished dithering and other stuff
   added test program
   changed name from pnglib to libpng
version 0.71
   changed pngtest.png for zlib 0.93
   fixed error in libpng.txt and example.c