Communal living companies are joining Airbnb, Lyft and other peer-to-peer marketplaces using sponsorship to promote their services.Companies in the category include P2P shared housing marketplaces (Roomi, etc.), co-living housing solutions (HubHaus, etc.) and other shared and short-term housing startups (Common, Ollie, Starcity, etc.).While their services all differ, they all target one primary consumer: Millennials.Roomi, for example, targets college students who live in (or plan to move to) Ne...