butterflies: vital rates changes

src/modules/butterflies/butterflies_generations.c

src/modules/butterflies/butterflies_main.c

src/modules/butterflies/butterflies_main.h

src/modules/butterflies/butterflies_overlays.c

src/modules/butterflies/butterflies_populations.c

src/modules/butterflies/butterflies_populations.h

src/modules/butterflies/butterflies_vital_rates.c