Add DLIB_JPEG_SUPPORT, DLIB_PNG_SUPPORT and DLIB_GIF_SUPPORT
Add DLIB_JPEG_SUPPORT, DLIB_PNG_SUPPORT and DLIB_GIF_SUPPORT

These flags will be added to *.vcxproj when using cmake
takuya-takeuchi/DlibDotNet,takuya-takeuchi/DlibDotNet,takuya-takeuchi/DlibDotNet,takuya-takeuchi/DlibDotNet