- Add --format-timestamp / -F CLI arg for batch and TUI timestamp
  conversion (e.g. nless --no-tui -F 'timestamp -> epoch' events.csv)
- Add :N% ex mode command to jump to percentage of file (e.g. :50%)
- Update docs across README, getting-started, tutorials, keybindings,
  internals, and help screen to reflect timestamp features and new CLI arg
- Close #52 with summary comment