Log file time display formats (delta time)

[cxong]

It would be very useful to be able to view log files containing timestamps, and reformat them in various ways. E.g.

• Time since last line (delta time)
• Time since a time reference

This is similar to what wireshark can do: https://www.wireshark.org/docs/wsug_html_chunked/ChWorkTimeFormatsSection.html

This may require several features to support:

• Regex match, without filtering (similar to #70)
• Parse regex match as a timestamp, given a strftime format string
• Reformat the timestamp:
  • given a strtime format string
  • as seconds from a fixed reference point
  • Options for reference point: epoch, start of file, start of page, user-specified timestamp
  • as seconds from last line

Would this be a good feature to have? If so, where could we start?