Pass the connection to hooks

Without this you cannot tell which connection has invoked the hook and cannot respond to the correct connection. You have to store the connection as a global variable and can only have one at a time or need separate hooks. Unfortunately this breaks the current API, but shouldn't be too hard to update, eg:
```lua
function bot.hooks.oldDebug(line)
    print(bot.conn.nick, line)
end

function bot.hooks:newDebug(line)
    print(self.nick, line)
end
```