fix possible division by zero in ccdemos/common_ply.h don't use DEFS variable in makefiles, just add it to CCFLAGS compile float version of libs with -fsingle-precision-constant

Makefile: added help and distclean target, plus small fixes ccdemos/common_sdl.h: print fps to window caption instead of console update and key callbacks fixed segfault when resizing window pressing c now causes print out of camera coordinates ccdemos/spheres_shadow.cc: controlling position of a light and focal length of camera