[libpng17] Added set(CMAKE_CONFIGURATION_TYPES ...) to CMakeLists.txt

(Andrew Hundt)
[libpng17] Deleted set(CMAKE_BUILD_TYPE) block from CMakeLists.txt
[libpng17] Fixed ICC compiler warning in tools/png-fix-itxt.c
[libpng17] Update README to delete CompuServ and add simplesystems.org
[libpng17] Deleted contrib/tools/fixitxt.c, which has been renamed.
[libpng17] Enclose the prototypes for the simplified write API in