Final Word: 'My Father's Name Was James Strom Thurmond'
Essie Mae Washington-Williams, 78-year-old retired teacher from Los Angeles, says she is daughter of late Sen Strom Thurmond and his family's black maid; makes announcement in Columbia, SC, where Thurmond was legendary political figure and, for decades, adamant segregationist; says she never sought to harm Thurmonds, who acknowledge tie, but needed to tell her own four children and now feels 'completely free'; photos; Thurmond had what Williams calls 'affair' with her mother, Carrie Butler, when she was 16 and he was 22-year-old teacher; statement confirms longtime rumors about woman who visited Thurmond in his Washington office and was supported by him throughout the years (M)