Build: Add integer version macro to jconfig.h This makes it significantly easier to do conditional compilation based on the libjpeg-turbo version. Based on: https://github.com/hasinoff/libjpeg-turbo/commit/e6d5b3e50b8b07488cb7b4d26ab2061685bc6875 https://github.com/hasinoff/libjpeg-turbo/commit/1394a89ba6f3cd8abb556c1b65bac4a5f09760d0 Closes #80