Added some imports to the world initialization code. I had to do this because you were not able to use the editor with the shooter demo map files without manually adding the imports to the map file. You do not have to do this now (note the TODO in the comments). I have also hard coded the camera zoom level to ensure the map editors zoom level at the time of saving the map is not used.

This demonstrates the use of PNG_USER_CONFIG and pngusr.h

To build a minimal read-only decoder, run
    gather.sh  # to collect needed files from pngminus, libpng, and zlib
    make -f makefile.std