Amperity is the latest company to join the Seattle region’s elusive club of unicorns, or privately held tech startups valued at more than $1 billion. The marketing startup just reeled in a $100 million investment round to boost its software that helps brands such as Alaska Airlines and Kroger organize and analyze individual customer data. The Series D round pushes total funding to date to $187 million and is yet another gigantic cash infusion for a Seattle-area startup.