This commit added functions working with fixed-size strings (non null-terminated also).
It's helpful for the following cases:
* getting key from substring without copying to separate buffer (better perfomance)
* using pure UTF-8 keys for the objets
* hack: set binary structs as the keys (see test_binary_keys)
added functions:
* json_object_getn
* json_object_setn
* json_object_setn_nocheck
* json_object_setn_new
* json_object_setn_new_nocheck
* json_object_deln
* json_object_iter_key_len
added iterators:
* json_object_keylen_foreach
* json_object_keylen_foreach_safe
Signed-off-by: Maxim Zhukov <mussitantesmortem@gmail.com>
