As he gears up for a year that includes touring with one of Nashville’s biggest stars, Vincent Mason is ready to establish himself as an expert craftsman of what he describes as “casual love songs.” Mason, who celebrated his 25th birthday last Monday, plumbs the depths of past heartbreak on “ There I Go ,” his riveting debut album. But the Georgia-born musician is also eager to put his past behind him and embrace the moment, and for good reason: His rich, soulful voice has already endeared him