Find json-c properly
#include <json/json.h>
doesn't work with newer json-c versions, the header is in json-c/json.h
User the location found by cmake, as in all other places json-c is used.
#include <json/json.h>
doesn't work with newer json-c versions, the header is in json-c/json.h
User the location found by cmake, as in all other places json-c is used.