Suggestion: Short flags for --min-time and --max-time + --last LINES

How about providing short flags for these `--min-time` and `--max-time`?

Possible options:

- `-n` for min, `-x` for max
- `-m` for min, `-x` for max
- `-m` for min, `-M` for max

Also - would be nice to have a flag that shows just the last N lines. Perhaps a `-l` (lowercase L) or `-n`, so we can simply `$ pt -l5`
