Function rsdb::c::rsdb_iter_next

#[no_mangle]
pub unsafe extern "C" fn rsdb_iter_next(
    iter: *mut TreeIter, 
    key: *mut *const c_char, 
    keylen: *mut size_t, 
    val: *mut *const c_char, 
    vallen: *mut size_t
) -> c_uchar

Get they next kv pair from an iterator. Caller is responsible for freeing the key and value with rsdb_free_buf. Returns 0 when exhausted.