Issue#114: check for the presence of isnan and isinf, and provide compat macros on MSCV where _isnan and _finite exist instead.

json_object.c

@@ -27,6 +27,7 @@
 #include "json_object.h"
 #include "json_object_private.h"
 #include "json_util.h"
+#include "math_compat.h"
 
 #if !defined(HAVE_STRDUP) && defined(_MSC_VER)
   /* MSC has the version as _strdup */