This patch provides a CMakeLists.txt file to build JSON-C library without relying on auto-tools support making the build a bit more portable and cleaner.

It can detect headers and symbols and generate config.h header file based on those detections. It cannot yet handle ctest(1) as the testing itself depends on comparing the output against files. Testing would need some creative abuse of CMake :)

The patch has been tested on GCC 4.8.5 (Linux), GCC 7.2.0 (MinGW) and Microsoft Visual C++ 16.0 (2010?).