This adds support for boolean, (unsigned) integers, and
null types. JSON_PRIMITIVE should be used as the type when
parsing and the value should be struct json_iter.
Once parsed the actual value can be obtained using one of
the primitive getters. If the type does not match they will
return false.
If using JSON_OPTIONAL with JSON_PRIMITIVE the resulting
iterator can be checked with json_iter_is_valid. If false
the key/value was not found or the type was not matching.
This is a minimal wrapper around jsmn.h to make things a bit easier
for iterating through a JSON object.
To use, first parse the JSON and create a contents object using
json_contents_new(). This object can then be used to initialize a
json_iter object using json_iter_init().
The json_iter object can then be parsed with json_iter_parse by
passing in JSON_MANDATORY/JSON_OPTIONAL arguments. Currently only
JSON_STRING and JSON_OBJECT types are supported. Any JSON_MANDATORY
values that are not found will result in an error.
If a JSON_OPTIONAL string is not found, the pointer will be NULL.
If a JSON_OPTIONAL object is not found, this iterator will be
initialized but 'start' will be -1. This can be checked with a
convenience macro json_object_not_found();
