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?).