Drew and Jennifer Burbridge, a married pair of documentary filmmakers, are suing the city of St. Louis after they were caught up by police sweeping protests downtown on September 17, sprayed with chemicals, beaten and arrested.A total of 123 people were arrested that night, all but three on charges of failure to disperse. Many have alleged that they were not given a way to leave the scene as police boxed them in using a tactic called "kettling," and then rounded them up indiscriminately.…