Recombining

od 0.2.1

• Updated od_disaggregate() so it's less likely to fail with unfathomable message (#30)

od 0.2.0

• New od_split() function, a copy of od_disaggregate()
• New od_aggregate() and od_group() functions (#24)
• Updated datasets for improved documentation and examples (#28)
• Updated introductory vignette building on the stplanr od vignette (#16)