We attempt to avoid splitting a log line between two files by detecting
if we are near the file size limit and scanning for new lines and only
flushing those.
BenchmarkRotator/1KB-8 300000 5613 ns/op
BenchmarkRotator/2KB-8 200000 8384 ns/op
BenchmarkRotator/4KB-8 100000 14604 ns/op
BenchmarkRotator/8KB-8 50000 25002 ns/op
BenchmarkRotator/16KB-8 30000 47572 ns/op
BenchmarkRotator/32KB-8 20000 92080 ns/op
BenchmarkRotator/64KB-8 10000 165883 ns/op
BenchmarkRotator/128KB-8 5000 294405 ns/op
BenchmarkRotator/256KB-8 2000 572374 ns/op