Update CMake scripts

[theta682]

1. Make CMake code style similar to standard CMake
2. Improve multi-configuration support: Add "d" suffix for Debug configuration
3. Improve detection of snprintf on Windows
4. Use BUILD_SHARED_LIBS to declare JAS_ENABLE_SHARED if it is defined
5. Reduce warning about GLUT on Windows

[mdadams]

I didn't have push access to your fork. So, I made some changes locally before committing.

[theta682]

Thank you.