Meta: functions for measuring intragroup dynamics

[robitalec]

trafficstars

Upcoming major release, with new functions for measuring intragroup dynamics (meta issue to track progress)

• [x] Position along group axis of movement, rank position
• [x] Group direction
• [ ] Time spent leading group
• [x] Distance, direction to leader
• [x] Directional correlation delay
• [x] Group centroid
• [x] Distance, direction to group centroid
• [x] Polarization
• [ ] Directional alignment
• [ ] Interindividual direction
• [ ] Behavioural zones
• [ ] Fission fusion