*** Costolo replaced Evan Williams as CEO of Twitter this week.  The big move comes at what might be an historic period for the social media giant.   In his role as COO of Twitter, Costolo had become known for pushing the advertising potential of the company.  In an interview with Ad Age's Abbey Klaassen at the IAB Mixx conference, Costolo said he and his fellow Twitter execs believe they have "cracked the code on a new kind of advertising."  And he talked about something called "promoted accounts."  Through using the same algorithms that help Twitter users connect with new people to follow through the "suggestions for you" feature launched this last summer, Twitter will help brands connect to the right people in the right way, Costolo says.  Here's video of the interview: