new zlib, better CMake integration, code cleanup

Improvements:
 - actually exports functions when compiling as a DLL
 - compiles without warnings, on 32bit and 64bit
 - when using CMake and VS, actually generate .lib files with names that
   get automatically imported.

Potential problems:
 - no more INSTALLing with CMake, pointless on Windows, and i think someone
   with better knowledge of Linux and Mac should implement this for those
   systems