Lower overhead than opening & reading from /dev/urandom, and works
in chroots and other situtations where /dev/urandom is not available.
Falls back to existing methods when kernel doesn't support the syscall.

Example:
mkdir build && cd build
cmake -DOVERRIDE_GET_RANDOM_SEED='do { extern uint32_t getMsTicks(void); int ms = getMsTicks() * 433494437; return ms; } while(0)' ..

The default is now that string data is stored inline at the end of json_object, though to allow for json_object_set_string() to set a _longer_ string, we still need to allow for the possibility of a separate char * pointer.
All json types have been split out now, next step it cleanup.

Tweak json_parse.c slightly to allow it to build against older json-c versions.

This is intended to provide a way, during development, to test out the memory
and performance impacts of a change.

This patch provides a CMakeLists.txt file to build JSON-C library without relying on auto-tools support. This makes 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 :) This will be provided a few patches later and may possibly involve refactoring test cases.

The patch has been tested on GCC 4.8.5 (Linux), GCC 7.2.0 (MinGW) and Microsoft Visual C++ 16.0 (2010?) locally. Also, compiles correctly on Travis CI and AppVeyor without errors.