[tail] Implement tail

[at15]

I could consider put into log package or have logx package where UI and tail etc. are provided ...
Come up with idea when looking at LISA18 - The History of Logging @ Facebook (Abridged)

Ref

• tail implementation in coreutils
• Video: FOSDEM 2017 about implementing tail -f in Go
  • https://github.com/fstab/grok_exporter/tree/master/tailer mentioned elastic beat, use polling, other use fsnotify, its implementation is similar to fsnotify and use syscall to watch stuff
• https://github.com/hpcloud/tail
• https://github.com/google/mtail extract whitebox monitoring data from application logs for collection in a timeseries database ??? (tsdb?)