kill-HUP reconfiguration support for logdo
detection of log falsification by message digest
countermeasure against log falsification
called by cron(8) support
The -b blocks and the -c bytes options like tail(1) support
The -F option like tail(1) support, does not close and reopen the file.
Ignore case and so on support
Implement of simple sed 's///' with boost xpressive only for study