With the economies of many African countries growing rapidly, the continent's cities are beginning to reflect the enormous potential for creating a new urban realm. Photo: © Damon Winter/The New York Times By mid-century, 60 percent of Africa’s booming and relatively young population will live in cities like this modern metropolis, which, with more than 5 million people, is now the second largest on the continent. Photo © Stanley Greene/NOOR A road near the dusty capital, a few months before South Sudan became the world's newest nation last year. Chinese investors have a jump-start here, as they do in much