Expand the pack/unpack API: json_(un)pack is the simple version with
no error output, json_(un)pack_ex has error output and flags,
json_v(un)pack_ex is a va_list version of json_(un)pack_ex.
Implement unpacking flags:
- JSON_UNPACK_ONLY turns off extra validation, i.e. array and object
unpacking doesn't check that all items are unpacked. This is really
just convenience for not adding '*' after each object and array.
- JSON_VALIDATE_ONLY turns off unpacking, i.e. no varargs are expected
and nothing is unpacked.
* By default, json_unpack() now checks that all items of arrays and
objects are unpacked. This is useful for validation.
* Add format specifier '*' to suppress this check for individual
arrays and objects. '*' must appear as the last format specifier
before the closing ']' or '}'.
