Optimize logging output

[mperham]

I noticed that setting the benchmark logger level to WARN, the jobs per sec went from 15k to 36k!

To reproduce:

1. Run make bench.
2. Edit bench/load.cr and change the log level on line 26 from INFO to WARN.
3. Repeat 1.

I optimized the Logger::Formatter here to stream to the IO but it didn't appear to make a difference. The logger is used here. Any ideas on how to minimize the log overhead?

[asterite]

I'll soon take a look, I'll try to run a profiler on it and see what can be optimized. It would be super cool to make it do more jobs per second :-)

[asterite]

I tried to optimize it but couldn't find a single bottleneck. The time is spread across converting the time to a string, appending to the IO, etc. I don't think there's much that can be done.

[mperham]

Ugh, it's such a huge difference; I'm surprised there's no low-hanging fruit to pick. Thanks for looking at it.

[mperham]

BTW I tried turning off the GC and it actually made it slower. Maybe heap size can affect performance? Logging appears to generate ~20% of the garbage.