[libpng15] Simplified read/write API initial version; basic read/write tested

on a variety of images, limited documentation (in the header file.)

scripts/symbols.def

diff --git a/scripts/symbols.def b/scripts/symbols.def
index 39466d4..564254f 100644
--- a/scripts/symbols.def
+++ b/scripts/symbols.def
@@ -239,3 +239,10 @@
  png_get_cHRM_XYZ_fixed @231
  png_set_cHRM_XYZ @232
  png_set_cHRM_XYZ_fixed @233
+ png_image_begin_read_from_file @234
+ png_image_begin_read_from_stdio @235
+ png_image_begin_read_from_memory @236
+ png_image_finish_read @237
+ png_image_free @238
+ png_image_write_to_file @239
+ png_image_write_to_stdio @240