[WIP] Add JSON deserializer yajl callbacks

This PR adds the JSON deserializer yajl callbacks with implementation.

Please review and tell me what is missing and what can be
optimized here.
 * You can simply use `strdup()`
 * Why are you doing this in `STATE_COMMAND_ARY_COMMAND_ARG_INDIRECT`? Maybe you meant `STATE_COMMAND_ARY_COMMAND_ARG_DIRECT`?