Stepcount

What's Changed
- Bumped `actipy` version to fix bug when input file too short: https://github.com/OxWearables/stepcount/issues/16

What's Changed
- Bump `torch` version to fix vulnerability bug.
- Add more specific version constraints in `setup.py`

What's Changed
- Additional summary metrics:
- Steps per day (min, med, max, avg).
- Walking per day (min, med, max, avg).
- Cadence (peak 1 min, peak 30 min)
- Use hyphen instead of underscore for output filenames: https://developers.google.com/style/filenames
- New entry point: `stepcount-collate-outputs` to collate outputs when processing several files.

What's Changed
- Fixed column names of output files ddbadca56983b3621da43de592fbd4421e1f1f47