json_int_t should be typedef'd as intmax_t

[jscott0]

Hello,
Currently the documentation says about json_int_t that "It represents the widest integer type available on your system." So by definition it's supposed to be equivalent to intmax_t. However, long long is not guaranteed to be equivalent to intmax_t. We should simply typedef json_int_t as an alias to intmax_t and forget about the nonsense of whether it's a long or long long.