Add option to overwrite logs

Add an option to make Tor overwrite logs, instead of appending them.

For instance whenever Tor gets restarted and this option is enabled the log does not get appended.*

This should enable operators to log without the risk of month old logs. Even when not enabled by default, what I was looking for in the first place, as I had not understood why logs are appending, it might help to have this option available.

The same applies to the client, once I was asked to provide logs from my client, and got told afterwards to remove the logging entry from torrc. When that does not happen, the client is logging for eternity and therefor provides an usage history due to the fact that the log is appending.

I couldn't pick "Tor" for "Component"; for me it's client and relay related.

*Other ways like, logging for a 24 hour period, keep this period and delete the lines that are older, might bring more problems than it's worth.