After months of speculation, it’s official: broadcast journalist Katie Couric will be leaving NBC’s Today Show at the end of May to anchor the CBS Evening News. As noted yesterday in the Washington Post, three women — Barbara Walters at ABC, Connie Chung at CBS and Elizabeth Vargas, at ABC’s “World News Tonight” — have co-anchored alongside men. This makes Couric the first solo female anchor of a weekday network newscast. Fishbowl DC has the…