repeat the latest command by dot

[akiradeveloper]

The current ijk does not implement . to repeat the latest command because simply repeating the latest log may be invalid. For example, delete 4 chars when there is only 3 chars in the buffer, what would happen? This may lead to SEGV.

An idea is that apply_log should return Result and when it is Err the editor state is restored and the repeat command only succeed the log returns Ok.