Previously we deinited backwards from the most recently heard message
until we reach a null-slot.
Now this code has been simplified to walk the backlog and deinit any
found messages.
This commit introduces a Bot struct which is the main type of this
project. The Bot holds a backlog of messages to be able to update a
typo in a message and so on.
So far there is no IRC/TLS implementation, it is only the base logic.
