Timestamp and performance improvements

The first commit yields a performance improvement for all cases by avoiding moment().

The second commit changes the format of the log output at the cost of partially neutralizing the performance gains from the first commit, though it is till faster over all.

The third commit removes the overhead of log rotation when log rotation isn't used. In the case of the benchmarks included in the repo, it's nearly a full order of magnitude difference on my computer.

Feel free to cherry-pick only the changes you want, I just didn't want to submit 3 different PRs for such small code changes.