Pass message callbacks through rc_hash_iterator_t

[Jamiras]

Deprecates rc_hash_init_verbose_message_callback and rc_hash_init_error_message_callback, which store callbacks in global variables and uses callbacks stored in the rc_hash_iterator_t instead.

For backwards compatibility, rc_hash_initialize_iterator will populate the iterator instance with the current global values, but they can be set/overwritten before calling rc_hash_iterate.

rc_hash_generate_from_buffer and rc_hash_generate_from_file are also deprecated as there's no easy way to pass the callbacks to them. Instead, a singular rc_hash_generate function is provided that will process an iterator for a specific console.